Introduction: Gray-B-Gon Wind-powered Evapotron for Graywater Disposal

Here is a wind-powered graywater evaporation device for your Burning Man camp. It will eliminate, legally and responsibly, all the wastewater produced in a medium-size camp, or several small camps. (Except for what belongs in a porta-potty.)

Burners dispose of their graywater in many ways, from "pack it out" to black-plastic-lined evaporation ponds to fullblown water-purification systems designed by professionals (who make coffee using their secondhand water!)

This device, the Gray-B-Gon evapotron, is the result of many years of using and improving. With typical winds, it evaporates or disperses fifteen to twenty gallons of water a day. (Maximum measured: 2 gallons per hour in high wind. Don't try this at home.) The rotating drum design avoids two performance killers of passive evapotrons: loss of wick absorbency, and reduced performance due to accumulated playa dust. Dust just washes off the Gray-B-Gon's drum, in a single rotation.

It's useful, and it's attractive! The flashing propeller blades and the slow-moving drum catch people's attention. The (almost always) excess capacity lets you offer graywater disposal to nearby camps, forming a neighborhood center the way village wells have done for millennia, only backward.

There are five subassemblies: the tray, two masts, the drum, and the propeller. During construction, you will assemble a complete evapotron (except for the black plastic tray liner and the panty-hose filter.) Once you've tested it in some wind, and it works, you can dismantle it (dismount the propeller and masts, and collapse the drum) for transporting to the playa. There, setting it up and putting it into operation takes under an hour.

As you prepare to leave the playa you dismantle it again, then lift the muddy plastic liner from the tray and dump it into your trash bag. With a water-spray cleaning, another old towel and a new plastic liner, your evapotron should be ready to go next year.

A word of caution

While you're enjoying watching and using your evapotron, keep in mind that graywater is unsanitary and can be hazardous to your health. Step 32 describes periodic disinfection with chlorine bleach. The subassemblies you take home are unsanitary too; but so is a handshake, or sharing eating utensils. If thinking about this makes you want to wash your hands, do it.

Time and Money

On your own, construction takes about a day or three. It uses common tools that are probably in your garage or shop, plus two or three you might want to buy. Materials cost varies, depending on what you have on hand, up to about $225.

Alternatively, join one of our one-day construction workshops, where we provide most of the parts at cost (around $75 including bike wheels) and the wood parts are precut. The construction time is one full day, less if you have friends helping. You provide a bucket and panty-hose.

Further Information
This guide has recently been revised to correspond to construction improvements and simplifications. Many of the illustrations have not yet been revised to match.
Please visit , which contains discussions, workshop dates, and other useful information. 8/14/13, 8/14

Step 1: Varnish -- the Secret of Long Life

A coat of varnish on wood parts will greatly extend their lifetimes. The desert is tough on wood, especially end grain and plywood edges. Your evapotron will last years longer if, before it's assembled, every wood part is sealed inside a plastic skin.

The finish I use is a water-based exterior polyurethane with a matte or satin finish (non-glossy). Water-based Varathane is one such product; it costs about $23 for a quart can (enough to cover three evapotrons). It's easy to apply, and doesn't require a skilled hand. You can coat all sides of a piece at one go, resting the piece on points or edges (just not a face) to dry. It dries rapidly to the touch; if you do your varnishing just before lunch, when you return the surfaces will be dry and workable. Water-based polyurethane has very little odor, and brush cleaning is easy. Do rinse out the brush thoroughly, several times, in clear or soapy water. Or,if you're going to do more varnishing the same day, you can put an unrinsed brush and a damp paper towel in a plastic bag, squeeze out the air, and refrigerate it.

Newly coated pieces will feel even rougher than before; that's because the surface fibers of the wood are now stiffer. A few strokes with sandpaper or a sanding block will smooth them down nicely.

Step 2: About Screws

Aside from the nameplate (which needs tiny #4 screws) and gussets (which need 1/4" bolts) everything is held together by screws of three sizes. Long screws are 3" long; Medium screws are 1-1/2" or 1-5/8" long; Short screws are 1" long.

Use construction-style wood screws -- phillips flathead, for easy driving with a cordless drill. Get screws rated for exterior use; they have anti-rust coatings. Avoid drywall screws, which rust quickly.

For driving 3" (#8) screws, first drill 1/8" pilot holes and 11/64" body and countersink holes.

For driving medium or short (#6) screws, drill 9/64" body holes. Driving a small or medium screw into a mast or a tray wall doesn't require a pilot hole.

A body hole lets a screw slide through the top piece of wood without cutting threads; a pilot hole lets the screw cut threads in the bottom piece. Working with plywood, it can be nearly impossible for a screw to draw two pieces tight, if threads cut in both pieces are keeping them apart.

Watch out for my favorite error: drilling a body hole through both top and bottom pieces of wood, rather than just the top piece. The bottom piece gets only a pilot hole.

When your top piece is plywood, you will need to use a countersink to give the screw heads space to sink down flush with the plywood's surface. If the screws in the tray's floor and especially the feet aren't countersunk, you risk scratching your car or whatever else the tray rests on.

Step 3: About Bike Wheels

Rims measuring 22-1/2" across are for 24" wheels; rims 25-1/2" across are for 26" and 27" wheels. You can use a mix of wheel sizes, but the two wheels that form the drum should have the same diameter. (Stand them on a flat surface, and see if the axles line up.) The propeller wheel must be a rear wheel (Step 4), but rear wheels are easier to use for the drum, too. Aluminum alloy rims are preferred; avoid steel rims (heavier; surface chrome-shiny, with rust spots) if you can.

Even some potato-chip wheels can be used as is, as long as they don't scrape. Or, you can try to detension, unbend, and retension them. Wheels can have some wobble (up to about an inch), rims can be cracked, and a spoke or two can be bent or missing; but the bearings must be usable. Bearings that are stiff, gravelly, or rattling may be fine once they've been greased and adjusted. Allow more bearing play than you'd tolerate in a wheel on a bike, 1/2 to1 full turn. All this requires a cone wrench and some bike mechanic skills.

Gear clusters must be removed. Mechanics can do this easily.

Rear wheels may be used as propellers or as drum ends. On a wheel used as a drum end, put a freehub or threaded hub on the inner face of the wheel. In Step 15 it slips into the PVC drum axle and keeps the axle centered.

Front wheels are used only as drum ends. On some front wheels, the drum axle will skate around on the spokes and won't stay centered. On such wheels, build a cage looking like a three-petaled flower of soft iron wire or 14- or 16-ga copper wire. Pick three spokes, more or less evenly spaced, close to the hub. Wrap wire once around one spoke, then guide it to the next spoke, leaving about an inch of "slack," then repeat on the third spoke, and around to the first again. Bend as needed to make a roughly triangular cage that fits the PVC pipe.

On the outer side of a drum end, a holllow wheel axle must extend at least 1/4 inch. [[ Outmoded instruction. ]] You may need to remove washers or spacers, or to "shift" the axle by loosening cone nuts and turning the axle while holding the cones still. These outer axles won't need nuts; they'll stay caged by angle brackets.

*=*=*=* Good News! That wheel is usable as is! No need to remove washers, shift axles, search for a nut matching the axle thread, and all that!

I recently realized that wheels with hollow axles are readily usable as drum ends, even if the axle protrusion is less than 1/4" -- in fact, even with no axle protrusion at all. Bend a skewer to make a slight but permanent bow. (I needed to use a shop vise to accomplish this.) Then align the hollow axle with the angle bracket's axle hole, and force the skewer into the axle. That's it; the skewer's permanently mounted.

Step 4: The Propeller Needs a Rear Wheel

The wheel for the propeller must be a rear wheel carrying a freehub (right wheel in picture), not a threaded hub left wheel in picture). In Step 22 you will make a pulley wheel that slides onto the freehub.

In Step 24 you will mount the propeller wheel by clamping it to a GA2 metal angle bracket. Your wheel may have a hollow axle and a quick-release skewer, which makes it easy (Step 13). If not, you will need one extra axle nut for the propeller. This can be either a heavy nut intended for clamping onto a fork, or a cone locknut -- thinner, but strong enough. There are many incompatible axle threads, so take your wheel with you when you scrounge for axle nuts.

On the side opposite from the freehub, you may need to remove a spacer or "shift" the axle to give the axle enough length to hold the GA2 bracket and extra nut. You may have to pry out and discard a sleek-looking rubber cover that almost-seals the bearing and nuts. (It's okay; some evapotrons operate for years this way.)

Most wheels have 36 spokes, and will carry 9 blades, each associated with a quartet of spokes. Most other wheels have 32 spokes, and carry 8 blades.

You can use a wheel with one or two spokes missing. When you reach Step 24, attaching blades to spokes, you'll find whether the missing spoke matters. If it's needed for a blade mounting point, cut a 14" length of soft iron wire. Bend or knot one end of the wire so it won't slip all the way through the spoke hole in the rim. Weave the other end past the crossing spokes and through the spoke hole in the hub, pull it taut and bend it over. Hard to believe, but it's sturdy enough to support a blade -- look at the picture in Step 26.

Step 5: Tools You Need

You will need these common tools for construction:

  • Drill, ideally a cordless variable-speed reversible drill.
  • Twist drill bits up to 1/4".
  • Phillips head bit.
  • Square: a try-square, framing square, or speed square.
  • Saw: a table saw or chop saw is good, but a saber saw or even a handsaw will work if you're careful.
  • Clamps.
  • Vise.
  • Shoe rasp, to round off 2x4 corners.
  • Scissors, bent-nose pliers, wire cutters.
  • razor knife / box cutter.
  • Adjustable crescent wrench for bolt heads and bike axle nuts.
  • marking pen.
  • Arrow stapler and a dozen staples, to lightly attach shims to tray walls.

You may also need these less common tools:

  • A step drill bit, for cutting large-diameter holes absurdly easily in sheet metal. We use it to drill or enlarge holes in metal angles to 13/32", to receive an axle; also to drill holes in a PVC bucket.
  • For making pulley flanges from plastic containers, a 1-3/8" fine-tooth (10 teeth/inch) hole saw for your drill. I use a DeWalt D1800221R.
  • A bike wheel cone wrench. A step in mid-jaw provides 4 jaw widths: 13, 14, 15, or 16 mm.

Step 6: Materials

  • matte or satin finish water-based exterior polyurethane varnish.
  • paintbrush.
  • masking tape, white or blue. (These instructions call it "blue tape" but you can use either.)
  • about 50 mini zip ties. Black stands up best to UV.
  • ball of light polypropylene twine, 400 ft or so. Hardware stores carry it. Polypro is strong but not stretchy, and on the playa resists UV degradation better than some other materials. To open the ball, DO NOT tear off the cellophane wrapper. Instead, poke a hole in the wrapper and fish out a loose end of twine.
  • cutting oil, for drilling in metal. 3-in-1 or WD-40 is better than nothing.
  • 30 medium (1-1/2" or 1-5/8") galvanized flathead drive screws.
  • 13 small (1") galvanized flathead drive screws.

For the tray

  • two 8-ft 2x4's, or enough material for two 45" lengths and two 29" lengths.
  • 1/4" exterior-grade plywood, 32" x 48" (one-third of a full sheet, less a 3" strip you can cut into staples).taktake with you
  • six builder's shims, about 16" long.
  • eight 3" galvanized flathead drive screws.
  • 28 medium (1-1/2" or 1-5/8") screws.

For the masts

  • 2x2, small tight knots ok, enough for a 5-ft and a 1-ft length. I have used common pine successfully.
  • 1/2" exterior-grade plywood, at least 11" x 25", for gussets and feet.
  • one metal angle bracket, Simpson GA2, for the propeller.
  • two metal angle brackets, Simpson A34, for drum wheels.
  • four 1" screws for mounting A34's.
  • twelve 1/4" carriage bolts 2-1/2" long, four washers and hex nuts, and eight wing nuts.
  • two 3/16" carriage bolts 1" long, and two nuts, for mounting the GA2 bracket on the propeller arm. A 3/16" thread may also be labeled as 10-24.
  • Two medium screws, for mounting the propeller arm on the power mast.

For the drum

  • 1-1/4" ID ("inside diameter") PVC pipe, 22" long.
  • 1" ID PVC pipe, 3-1/2" long.
  • 80 ft. of light polypro twine (from ball, above).
  • two bike wheels of the same size.
  • tulle (polyester or nylon mesh), 2-1/2 yards, available at fabric stores. Cutting a full width (54" or so) lengthwise gives you two usable panels about 27" wide. Get the finest mesh available.
  • mini zipties (in Materials, above).

For the pulley wheel, propeller, and drive belt

  • one bicycle rear wheel with either a threaded hub or preferably a freehub.
  • one extra axle nut, or one quick-release skewer and nut.
  • aluminum sheet, enough for five 9"x12" or 8"x12" pieces depending on wheel size. Ask for 12" flashing at a hardware or building-supply store.
  • thin cardboard for blade template.
  • emery cloth.
  • 30 mini zip ties (in Materials, above)
  • 1-1/4" ID PVC pipe, 1" long.
  • 5-1/4" 3M "Safety Walk" gray anti-slip tape, 1" wide. Hardware stores sell it by the foot.
  • two plastic (#1 PETE) tubs intended for deli food containers, 8 oz capacity or more. They're UV resistant and have curving shoulders.
  • two nylon stockings or sheer panty-hose legs. Ladders and holes are ok.
  • 2-3 ft 12-gauge copper wire, bare or insulated, for propeller balancing.
  • for freehub propeller wheel: 1 ft. bare 16-gauge copper wire.
  • for threaded-hub propeller wheel: 1 ft. bare 20-gauge copper wire, and a bottle of Gorilla glue. The copper wire is available in hardware stores. The 16- and 20-gauge copper wire is also available in craft stores.
  • Propeller mounting takes less time and effort if you have a hollow axle and a quick-release skewer and skewer nut.

On the playa

  • tools, including a cordless drill and bits, and an adjustable crescent wrench.
  • nuts, bolts, and washers for connecting mast & gusset assemblies to the tray.
  • 5-gallon plastic bucket.
  • spare zip ties.
  • one pair of panty-hose with no holes above the knees.
  • light polypro twine (leftover ball from drum building).
  • 3 or 4 mil black plastic sheeting, 42" x 54" .
  • eight 1-1/2" square plywood staples, cut in Step 7.
  • eight 1" screws (8 of the 13, above).
  • bucket cushion: fabric (towel, clothing, burlap, etc.) scrap, 14" square or larger.
  • fresh 2-qt jug of Concentrated Clorox Regular Bleach. See Step 32 for info on chlorine bleach and how to apply it.

Step 7: Cut Wood and Varnish It


  • Cut 1/2" plywood into three trapezoids (corners trimmed) and four rectangles.
  • Cut 2x4's for tray frame.
  • Cut 1/4" plywood for tray and staples.
  • Cut 2x2's for masts.
  • Sand edges and varnish all wood pieces.


  • 1/2" exterior-grade plywood, 11" x 25" or larger.
  • 1/4" exterior-grade plywood, 32" x 48".
  • two 8-ft 2x4's, or enough material for two 45" lengths and two 29" lengths. If you can, avoid pieces with warps or twists.
  • common pine 2x2, 6ft.

Cut three trapezoids from 1/2" plywood, and remove 3/8" from the sharp corners. Trapezoids will become one propeller arm and two gussets for the masts. Cut four rectangles, 1-1/2" by 6" or so, for feet under the tray's corners.

Cut 1/4" plywood as shown, to produce a 32" x 45" tray floor and eight 1-1/2" squares (which I will call "plywood staples").

Trim 2x4 mill ends, then cut into two 45" lengths and two 29" lengths. These are the only wood cuts that must be exactly square. Use a table saw or chop saw for this.

Cut the 2x2 into two lengths:
60", which will become the "power mast,"
12", which will become the "idler mast."

Sand corners and edges to round them. Stack the 8 staples and drill a 1/8" hole through the centers.

Spread a drop cloth and varnish all pieces, especially end grain and plywood edges. (Yes, this really is a time-saver, compared to replacing checked, delaminating, and splintery parts a year from now.)

Step 8: Make the Tray Frame

Materials: 2x4's, eight 3" screws.

Using the 1/4" plywood tray floor as a work surface, arrange the frame 2x4's with end (29") pieces inside the side (45") pieces. If you have long bar clamps, lightly clamp the side pieces near top and bottom, then tap end pieces into alignment. The frame should align with the edges of the tray floor without much forcing. If it insists in rising out of plane, apply Step 9. If the frame wants to form a parallelogram (in the plane), it'll be easily un-distorted when the floor gets attached.

At each corner, drill pilot and body holes, and screw in two 3" screws, but don't tighten them fully until the end of Step 9.

Step 9: Fixing Skews and Twists

Check each corner for squareness. Attaching the tray floor in Step 10 will correct minor skews, but if a mild push won't square up a corner, loosen the screws and insert a shim piece vertically in the outer or inner side of the joint. A staple or a dab of glue will help keep the shim in place.

The tray may take on a twist during assembly, resisting all efforts to make it lie flat -- and lying flat is an important feature for a shallow tray holding water. The twist can arise from slightly non-straight wood, from ends cut slightly non-square, or from joints not quite aligned by screws.

Loosen all screws. At the two diagonal corners that are too high, remove the bottom screws. As you hold the frame flat, slide builder's shims into the wide ends of any gaps. Drill a body hole through the shim, to reduce splitting, and reinstall the bottom screws. Tighten the screws; the frame should now lie substantially flat. Saw the shims flush.

Step 10: Make a Deep End and Assemble the Tray


  • four builder's shims, about 16" long.
  • Arrow stapler and 3/8" staples.
  • about thirty medium screws.
  • #6 countersink bit, or 3/32" and 9/64" bits and a countersink.

Assemble the tray on the 2x4 frame.

Lay a pair of builder's shims on each side rail, with thick ends butted together about 16" from one end of the tray. These shims will create a "deep end" of the pool beneath the drum. Staple each shim twice.

Lay the 1/4" plywood floor on the 2x4 frame. Lay plywood feet on each corner, along the top and bottom edges. Look at the diagrams below for screw placement; make sure you will hit each shim and foot with at least two screws.

Some 2x4 frames resist having perfect 90-degree corners. Use this drilling plan to encourage square corners and to minimize pilot-drill bit breakage. Line up the frame and floor at just one end, clamp, and either drill 7 countersink holes, or drill 7 pilot holes; enlarge the holes in the feet to 9/64" body holes, and drill countersinks so the screws will lie flush. Drive screws. At the opposite end, persuade the frame and floor into alignment; clamp them, and drill and screw them together. Finally, drill and screw the sides, and turn the tray face upward.

Step 11: Mount the Power and Idler Masts

Summary: Drill bolt holes in two trapezoids, and mount them to the tray and masts.


  • two 1/2" plywood trapezoids (gussets for masts).
  • 2x2's, 12" and 60" long (the masts).
  • twelve 1/4" carriage bolts 2-1/2" long, with 4 washers and hex nuts, and 8 wing nuts.

Drill body holes for 1/4" bolts in the two gussets, as shown in the Hole Location drawing. In one gusset, drill one of the bolt holes distinctly out of position, so that when you dismantle and later reassemble your evapotron you can't mount the masts on the wrong sides. Note: these four bolts are inserted and removed repeatedly; this will be easier if you clean out the 1/4" holes in the gussets and the 2x4's, by pushing the drill bit in and out several times.

Position a gusset on the outer face of the tray, over the "deep end" shims, centered 15" from the tray's outer end. Align the gusset bottom edge with the 2x4 bottom edge (not the plywood floor's bottom edge), and clamp it in place. With the gusset holes as a guide, drill only one bolt hole through the 2x4. Insert a carriage bolt from the inside of the tray and tap it home with a hammer. Add a wing nut and hand tighten. (A fine detail for bolts that will be repeatedly inserted and removed: a carriage bolt has four square shoulders under its rounded head. These form a square indentation that's worth preserving. When re-inserting a bolt, match the indentation's orientation; better yet, always insert bolts with one shoulder facing directly upward.)

Repeat with the other three bolts; then repeat on the other side with the other gusset and mast.

Stand a mast on the tray rim, centered on a gusset; clamp loosely while you square the mast with the tray, then tighten the clamp. Drill a 1/4" hole through the mast, insert a bolt from inside, and add a washer and hex nut. Repeat with the second mast bolt.

Repeat with the other gusset and mast.

Step 12: Drill the Metal Angle Brackets

Summary: In each angle bracket, drill or widen one hole for an axle and enlarge two holes for screws or bolts.


  • one Simpson GA2 and two Simpson A34 angle brackets, or equivalent.
  • cutting oil.

The angle brackets need holes for wheel axles. On the wide face of each A34 bracket, drill a 13/32" hole, more or less centered.

The GA2's center hole is perfectly located for widening. If your propeller wheel has a hollow axle and a quick-release skewer, drill out the GA2 center hole only to fit the skewer, 13/64". Otherwise, widen it to 13/32", to fit the axle.

The A34s already have holes suitable for screws. On the GA2, on the other face from the axle hole, widen the top and bottom holes to 3/16".

If you're not experienced in drilling through sheet metal:

  • Make a dimple where the hole is to be, using a hammer and a centerpunch or large nail.
  • Drill a small-diameter hole first, then enlarge it with larger bits.
  • Keep the bit tip wet with cutting oil (or 3-in-1 or WD-40 as a second choice) to ease the work and save drill bits.

The best tool for enlarging is a step drill bit, and this project is a good excuse for buying one. If you're undertaking this job with just twist drill bits, use a sequence of larger and larger bits, drilling from both sides of the metal alternately. Keep your vise jaws tight and maintain a good grip on your drill.

Step 13: Mount the Propeller Arm


  • propeller arm trapezoid.
  • GA2 angle bracket.
  • two 3/16" carriage bolts, length 1", and two wing nuts.
  • two medium screws.

Align the GA2 bracket with the short end of the arm trapezoid and drill one body hole (3/16") through the arm. Insert a bolt from the plywood side and tap it home with a hammer; then add the bracket and a wing nut. Repeat with the second body hole, bracket, and wing nut.

Drill two 9/64" body holes for medium screws. Clamp the arm to the power mast near the top and drive one medium screw.

The angle bracket needs to tilt slightly downward -- if you have a spirit level, less than half a bubble. Here's why. In operation, the drive belt lifts some water up to the pulley wheel. The tilt is to allow the water to drip off the pulley rather than flowing into the wheel's hub and out the spokes to the rim, where it can fling off and land on nearby participants.

Drive the second medium screw.

Step 14: Make the Drum: Cut PVC Pipe

Summary: Cut a 1" length of 1-1/4" ID PVC pipe, for the pulley groove. Cut another length, 22-1/8"+kerf, for the drum axle. At 2-5/8" to 2-1/4" from one end of this axle, cut it at an angle of 14 degrees. The beveled cut makes it easier to re-erect the braced and laced drum, after it's been collapsed for storage.


1-1/4" I.D. PVC pipe with precisely squared ends, length 23-1/8" + 2 kerfs. (Kerf = saw blade thickness, typically 1/16" or 3/32".)
1" I.D. PVC pipe, 3-1/2" long. (The "keeper.")
blue tape.


accurate saw: table saw, chop saw, or backsaw.
rasp or coarse sandpaper.

Measurement gets tricky here. A single cut at 14 degrees will produce two pipe pieces, each with one beveled end. You may not get exactly a 14-degree bevel (which isn't important), but both pieces will have exactly the same bevel (which is).

Start by checking one end for squareness (cut if necessary.) Cut off a piece exactly 1" long, and save it for the pulley. If you have a table saw or a chop saw, it's easy. To cut a pipe evenly with just a handsaw or backsaw, start by wrapping blue tape evenly around the pipe, with the tape located on the measured side of the cut line (not on the scrap piece). Then, rather than sawing through, saw just enough to start a groove alongside the tape edge. Rotate the pipe and saw a bit more, and continue around the pipe until it's done. Finally take a rasp or coarse sandpaper to the new-cut ends, to remove any irregularities.

Measure and cut the other end square at 22-1/8 + kerf.

The next cut is diagonal, at 14 degrees; the longer and shorter sides will differ by about 3/8". Cut to produce a maximum length of about 19-5/8". The short piece that remains will measure about 3" at the longest and 2-5/8" at the shortest.

For a freehand angled cut, place one corner of a scrap of blue tape at 19-5/8", and halfway around place another at 19-1/4". Lay down a length of tape from one tape corner to the other. Clamp the pipe with the tape length facing upward, so your sawing starts at the midpoint. Saw without rotating the pipe, but check often that the saw's going where you want it.

Use a rasp or sandpaper to round down the inner edge of the 2-1/2" pipe's beveled end. Round down the keeper's outer edges at both ends. You now have parts for a drum axle that will be both stable for use and collapsible for storage.

Step 15: Make the Drum: Mount the Wheels and Axle

Summary: mount wheels on masts; assemble PVC axle between them.

• two bicycle wheels with the same diameter.
• two Simpson A34 angle brackets or similar, drilled to receive axle ends.
• four 1" screws.
• 1/4" plywood scraps.
• PVC axle parts: short, long and keeper.

Tools: clamps, or helper, and drill.

Drum assembly doesn't depend on precise measurements. It relies on mounting, adjusting, and remounting wheels until you're close enough. Place a scrap of 1/4" plywood in the tray, under the power mast. Rest one wheel vertically on the scrap, with axles facing outward and any freehub or threaded hub (if it's a rear wheel) or wire cage (if it's a front wheel) facing inward. Slide an A34 angle bracket over the outer axle end, and place it against the side of the power mast that faces the tray's long end. Clamp it in place and screw a single 1" screw through a hole in the angle bracket.

Repeat with the idler mast and the other wheel and its angle bracket, but defer driving another 1" screw while you assemble the PVC drum axle:

  • place the short beveled pipe over the wheel axle,
  • slip the keeper in,
  • add the long pipe.

If either wheel has a threaded hub, you may need to force or twist the pipe over it. When you position the angle bracket on the idler mast, push the bracket inward and pull the idler mast outward, to reduce play. Finally, drive the deferred 1" screw through the angle bracket. The two single screws can be rotated, to help fine-tune the angle bracket height.

Remove 1/4" scraps, and give the drum a slow spin. If no rim scrapes the floor, it's good enough. Fix scrapes by rotating angle brackets upwards. Drive one more 1" screw through each angle bracket.

Step 16: Make the Drum: Install Bracing Twine


Tether bracing twine to eight points on the rims, to make the drum rigid.


  • two wheels and PVC axle mounted loosely on masts, following Step 15. Each wheel must have either 32 or 36 spokes.

  • two 15-ft lengths of twine.

  • eight zipties.
  • blue tape.

  • four mini-bungies.

You will need to know some knots: the overhand knot (to keep twine from unraveling); the overhand knot on a bight (that is, tied in doubled twine, to form a permanent loop); and a slip knot under tension (pinch the twine crossing with a finger and thumb, then tie an overhand knot without letting the twine end slip through.)

Mount the wheels and PVC axle as in steps 14 & 15. Initially the wheels are unsupported and uncoordinated. To keep them in sync, stretch two or four mini-bungies between the wheels, hooking on to spokes close to the hubs. For brevity I’ll call the two wheels Near and Far. The names stay with the wheels, no matter where you stand or move.

Place blue tape flags on four evenly-spaced spokes of Near. On a 36-spoke wheel, the flag positions are nine spokes apart; on a 32-spoke wheel, eight spokes apart. Make one flagged spoke point straight up. Place flags on four of Far’s spokes, aligned with Near’s flags.

In one 15-ft twine length, tie an overhand knot at one end, and at the other end tie an overhand knot on a bight to make a loop. Use blue tape to fasten the loop temporarily to the midpoint of the PVC axle. Begin the first tether: stand facing Near and lead the unlooped end out toward yourself, between the top flagged spoke and an adjacent spoke. Follow the “wind, U-turn, counter-wind” path shown in the figure and pull all the loose twine through.  [Fig.1: One tether, as viewed from the drum’s centerline]

You’re ready to wind the second tether, which will be on Far, one flagged spoke away from the first tether. Never go directly across, or to a flagged spoke that’s already occupied. The twine path alternates between a horizontal flagged spoke and a vertical. The U-turn always goes around a flagged spoke.

If you see twine crossing itself, undo and retry the operation in the opposite direction. If you find you picked the wrong spoke, or wound the wrong side of the right spoke, back up and retry.

Continue similarly with a third tether, alternating horizontal and vertical flagged spokes. Make sure the bungies are maintaining the wheels’ relative orientation. If the twine or the flags seem discombobulated, undo some or all the twine and start fresh. This is often easier than diagnosing what went wrong.

In the fourth tether you will meet the twine’s starting point, the loop taped to the PVC axle. If your twine hasn’t crossed itself anywhere, then you’ve done all this correctly. Pull the loop free from the axle, push the overhand knot through the loop, pull it gently to remove slack, then pinch the crossing and fasten the ends with a slip knot.

Repeat the tethering process with the other length of twine: knot its ends, tape the loop to the PVC axle, and pick any unoccupied flagged spoke (there are four) to start with. This time, twine does cross twine to form X’s floating inside the drum. When all tethers are complete, wiggle the wheels into alignment, even out the slack, and tension: have your helper hold both wheels by the rims and rotate them back and forth a few inches. Release and retie the slip-knots to remove slack. (But don’t raise the tension yet.)

Check that in each tether the twine U-turn rests against the rim and the side of a spoke nipple, and isn't hung up on the end of the nipple. Note that each tether has formed itself to have two nearly parallel twine strands crossing the rim’s channel.

To unite the elements at each tether, place a ziptie in the rim's channel, with one crossing strand going over it and the other crossing strand going under it. (The top pink ziptie in the image.) Holding the ziptie's ends, slide it sideways over the rim toward the drum’s centerline, until it meets the flagged spoke. Surround the spoke and the two diagonal strands and engage the ziptie, but leave it about 1/4 inch loose. If the tension feels excessive, untie the slipknot and retie it. Repeat on the seven other tethers.

Now to align the wheels. You can't true them, but you can prevent them from scraping the tray walls, which really is all that matters. Spin the drum. Is there a major wobble? Stop the drum when the wobble’s near the bottom. Using your helper, or a wood block between the wheel rim and the tray wall, push the wobble inward. Find a tether involved with the wobble that now has one diagonal strand tight and the other slack. Lift the crossing strand with too much slack, then release it while you lift the other strand and release it. You have averaged out unequal tension while diminishing the wobble. Repeat as needed; finally, remove the bungies. Leave the twine loops permanently floating inside the drum, where they’re accessible if you ever need to make adjustments. Pull all 8 zipties somewhat snug. Snugness preserves the drum’s integrity when it’s collapsed for transportation, but makes later adjustments more difficult.

Step 17: Make the Drum: Lace Zigzag Support

Summary: Build support for the tulle surface by lacing twine zigzag.


  • 50 ft of polypro twine.
  • small plastic bag.

Tie an overhand knot in doubled twine (bight) to form a loop. Put the twine ball in a small plastic bag, mash it flat, and see if it will slip between spokes. If it will, temporarily attach the loop to the rim, and lace by moving the twine ball. If the ball won't slip between spokes, you'll have to leave it at the starting point and repeatedly pull twine through the whole path.

Stand at the idler mast and zigzag loosely around the wheels. The first zig goes between spokes and under the rim of the near wheel, then not straight across, but two spoke spaces to the left of straight across, under the rim of the far wheel. The first zag returns over both rims, not straight across but four spoke spaces to the left of the starting point on the near wheel. Each successive zig or zag goes four spokes to the left of the previous zig or zag.

Why? Starting two spokes over evens the torque. Lacing straight across to begin would induce a rotational torque from all the zags; you'd see half the twine braces taut and the other half sagging loose.

You may have wheels with different numbers of spokes. If the far wheel has 36 spokes and the near one has 32, then every quarter of the way around, make one zag that advances on the near wheel by only three spokes, and you'll come out even.

When the twine meets its starting point, cut the twine, knot the end against fraying and put it through the loop. Tension it mildly. Repeatedly tension the lacing by "plucking" your way around, removing small amounts of slack at each step until the drum's almost taut. (Really taut would make the collapsible axle difficult to reinstall.) Secure the loose end with a slipknot at the loop.

If at any point you need to cut the twine, or need to add another length to it, go ahead. Knots will remain undisturbed underneath the tulle and cause no problems.

Now the angle brackets may hold the wheel axles rather loosely. If axial play is more than 1/4", it may bring a wheel axle close to falling out of its bracket. Correct by moving one bracket slightly inward. Are the screws centered on the masts, or too close to the edge? Use other bracket holes. Do the wheel rims clear the tray floor equally? Check that the angle brackets are holding it level, and that both wheels have similar clearance from the floor, about 1/4 inch. Reposition angle bracket(s) to correct.

When you're satisfied, drive a second screw into each bracket.

Step 18: Make the Drum: Cover With Tulle

Summary: Add a bulge and cover the lacing with tulle.


  • Tulle, 2-1/2 yards, black, from a fabric store.
  • Tulle scraps: any colors, about a half yard of each.
  • 12 mini zip ties.

Now you need a panel of tulle 27" wide. Tulle usually comes about 54" wide; if so fold it lengthwise and cut it in two. Set aside one panel as a spare. Wrap the other panel loosely around the drum once, to find the length, and trim the excess fabric from one end.

Using your tulle scrap, or a piece of tulle of contrasting color, anchor one end to a spoke. Keeping it loose and fluffy, wind half the length around a few spokes' worth of rim. Continue winding as you move back to the starting point. Ziptie the two ends together. You have produced a caterpillar-like bulge that will brush the tray floor to mop up the last bits of graywater. Use the second scrap on the other wheel.

In the rest of the process, as you fasten the tulle panel, resist the temptation to tension the fabric so it looks unwrinkled and elegant. Tensioning simply brings the fabric closer to tearing. On occasion you may need to reach inside the drum, for instance when you're erecting the 3-piece PVC axle. A tulle edge that's slightly floppy is easier to slip a hand past.

Anchor one end of the tulle panel by zip-tying a corner to each wheel. Pull the mesh sideways only as needed to extend to the rim, then poke a hole about 3/4" from the edge, using a zip-tie's tail or other pointed object. Zip-tie through the hole and around the nearest spoke. Make sure each sharp-cornered zip-tie head lies close to its spoke, where it won't come in contact with the black plastic tray liner.

Wrap the tulle panel around the drum. Anchor the free end with another pair of zip ties. Add two more zip ties at halfway around, then at 1/4 and 3/4. Clip off tails.

Step 19: Make the Pulley Wheel: Prepare the Groove and Flanges


  • 1" length of 1-1/4" PVC pipe.
  • alcohol.
  • paper towel.
  • 5-1/4" of 1"-width 3M gray nonslip tape.
  • SOLO (or other) PETE 8-oz or larger deli food tubs with rounded walls.


  • Scissors or box knife.
  • Marking pen.
  • 1-3/8" fine-tooth hole saw.

In rigging terminology, a pulley has a groove flanked by two flanges. The groove is what the rope bears on. On a Gray-B-Gon, the groove is a 1" length of PVC pipe with a nonskid surface, and the flanges are plastic container bottoms.

Clean the surface of the PVC pipe length with a paper towel and alcohol, and let it dry on a clean, flat surface. Measure and cut a 5-1/4" length of anti-slip tape. Peel about 1" of the backing and fold it back. Avoid letting the adhesive touch anything.

Place the tape on edge beside the 1" pipe. Success now depends on avoiding accidental contact with the adhesive, and on keeping the tape edge in light contact with the flat surface, for alignment.

Press the folded backing against the pipe, then slide your finger toward the exposed tape end. Once the tape end sticks, pull the loose end of the backing to expose more adhesive. Press this exposed adhesive against the pipe, rotate and repeat. When it's fully mounted, you should see a gap of about 1/32".

You will find ideal flanges in your grocery store: deli tubs, with rounded walls, that once contained olives or other delicacies. Look for an eight-ounce tub; deeper tubs must be cut down, which sacrifices strength. Don't use tubs with straight walls that extend below the bottom to form a strengthening ridge. The rounded wall defeats the drive belt's attempts to climb off the flange.

Tubs made of "PETE" (polyethylene terephthalate, icon "1" in the recycle triangle) look flimsy but resist weathering and UV. Tubs made of polypropylene ("PP", icon "5") look almost identical but shatter easily. Avoid containers with irregular or deeply lobed floors.

First cut a 1-3/8" hole in the center of the tub's floor with a fine-tooth hole saw. Don't worry if the hole isn't precisely centered. If you've got an 8-oz tub, you're finished. If you have a deeper (16, 24, or 32 oz) tub, cut the walls down to 5/8": hold a marking pen against the tub at 5/8" while you rotate it, then cut as evenly as possible.

Step 20: Make the Pulley Wheel From a Freehub-style Wheel


  • one rear wheel and either one extra axle nut or a quick-release skewer and nut.

Choose step 21 or 22 according to the type of hub: threaded (on left in picture) or freehub (on right). Build a pulley on a non-freehub wheel only as a last resort. Freehub rear wheels are ubiquitous; bike shops or co-ops discard them every day. Ask at bike shops or co-ops, or check their dumpster regularly.

Step 21:

Step 22:

Step 23: Make the Pulley Wheel for a Threaded Hub (not Recommended)


  • pulley groove (1" PVC pipe with no-slip tape).
  • outer and inner flanges.
  • 20-gauge bare copper wire, 9".
  • Gorilla glue and applicator such as a coffee stir stick.

Use an old toothbrush and cleanser to clean the threads on the hub, and let the hub dry.

Using the outer flange as a guide, mark one end of the 1" pipe at 5 equally-spaced points. Transfer the marks to the flange. Drill 3/32" holes at the marks, 3/16" in from each end of the pipe. Drill 5 holes through the outer flange, 3/16" out from the inner edge.

Now you will attach the outer flange and the 1" pipe. With needle-nose pliers, thread the 9" copper wire half its length through a hole in the pipe and a hole in the flange, with the flange's raw edge facing away from the pipe. Continue threading spirally, with the two ends of the wire moving in opposite directions, until the ends meet. Copper wire will work-harden, so minimize the bending; make gentle curves in the wire and don't draw it up tight yet.

Working again from the center of the wire, cinch each segment of the wire somewhat tight, removing kinks as you go. Twist the ends together.

Spread Gorilla glue to fill the hub's threads, and dot glue on the inside of the pipe at each of the five holes at the other end from the wiring.

Press and twist the wired-up assembly onto the hub. Let the glue cure for several hours. Gorilla glue expands as it cures, and may ooze through the holes to create mounds on the pipe surface. Scrape these off after about a half hour, before the glue hardens.

Step 24: Make the Pulley Wheel for a Freehub


  • pulley groove (1" PVC pipe with nonslip tape)
  • two flanges
  • 16-gauge bare copper wire, 12"

Cut three 3-1/2" lengths of bare 16-gauge copper wire, and hook them to spokes around the freehub. Bend the wires so they lie in the recesses of the freehub splines. Slide on the inner flange, then the pipe. Usually this is a good fit, but PVC pipe varies and it may be a tight fit. If so use a wood block and a hammer to get it seated. If you ever need to remove the pipe, I have succeeded by prying with a smallish pry-bar-like tool and a block of wood for a fulcrum, working my way around.

Mount the outer flange and bend over the ends of the three copper wires against it.

Step 25: Propeller: Make a Blade Template


  • card stock (manila folder) or thin cardboard (cereal box)

Wheel sizes, spoke numbers, and spoke patterns vary. The exact layout described here may not work on your wheel, but something similar will. The goal is to attach aluminum blades that angle outward on the front side, and are restrained by spokes from extending at all from the back side (the side with the pulley wheel.) Strong winds can blow the stocking drive belt against the back of the wheel. Hitting the spokes is harmless, but hitting blade after blade coming edge-first isn't.

Measure from the rim to a spoke crossing about 2" from the hub and add 1/2". You will probably choose this as the blade length -- if blades extend past the rim, the propeller is more awkward to transport. But if you like the look of larger blades, as in the Step 6 image, then cut them longer.

The image below shows how two blades for a 27" or 26" wheel can be cut from a 12 x 9" sheet of aluminum. For a 24" wheel, make the blades shorter and use a 12" x 8" sheet of aluminum.

You will need nine blades for a 36-spoke wheel, or eight blades for a 32-spoke wheel. For a 24-spoke wheel (rare and unusual), you may want a shape that's about an inch broader.

Draw and cut a blade template of cardboard, try it in Step 22, and when you're satisfied cut a trial blade from aluminum. You don't need tin snips; good-quality scissors will do the job.

Step 26: Propeller: Pick Mounting Points and Cut Blades


  • trial blade.
  • bike wheel with pulley wheel mounted.
  • aluminum sheet, enough for five 9"x12" or 8"x12" pieces. A roll of aluminum flashing, available at hardware and building supply stores, is a good thickness.
  • medium-grit emery cloth.
  • mini zip ties.
  • marking pen.

Clamp your wheel upright, with the pulley wheel facing you, and think of the pulley side as the back face of the propeller. Position your trial blade like the annotated blade image. The blades are pressing against the spokes on the front face of the wheel; zip ties will hold the blades to the spokes.

With one thumb or finger, press the blade against the spoke crossing ("first mounting point."). The crucial spoke is the one at about 10:00 -- it cages the blade within the spoke line.

Find a second point on the blade to press, farther out, that will encourage a curve that makes the blade arch out in the front at about 30 to 45 degrees. (The "second mounting point.").

If this layout doesn't work on your wheel, it may be due to an unusual spoke pattern. Try the mirror image, or find another shape or position that does work. Cut a new trial blade if necessary.

Press the trial blade into the spokes. Mark the blade with a dot at each side of the spoke crossing and at each side of the second point. Drill 1/8" holes at the dots. From the front, slip a zip tie through a hole, around the spoke and back through the other hole, and cinch it up. After zip-tying two points, you may find you need a third point anchored to get the shape you want.

Look the blade over. The curve and angle may be okay, but the blade may be too long, or not long enough, or the back edge may be sneaking past the spoke line. Use the marking pen to show the needed changes, sever the zip ties, and cut and drill a new and improved blade shape.

Once you're satisfied, use the blade as a template to draw eight more shapes, and cut them out. (Or seven more, for a 32-spoke wheel.) Smooth all the edges with emery cloth, so your propeller won't draw blood.

Step 27: Propeller: Drill and Attach Blades

Stack the blades with the template blade on top, clamp them with at least two clamps, and drill 1/8" holes through the stack. Mount the blades on the wheel, starting all zip ties on the front faces so they can't snag the drive belt in a wind. Snug them down with low tension, and trim the loose ends.

Step 28: Propeller: Mount It and Balance It


  • 2-3 ft 12- or 14-gauge copper wire, bare or insulated.
  • blue tape.

Mount the propeller on the arm. Is it balanced? If not, some copper wire will fix it. The balance doesn't have to be perfect, but the better it is, the more readily the propeller will turn in light winds. The length of time the wind turns the propeller, not the speed it turns at, is what governs the rate of water disposal.

Do this step indoors, or on a day with no wind at all. Measure from the wheel axle to the rim, and cut a wire to that length. Coil it to make a compact bundle. With the unbalanced wheel at rest (heavy side down, in other words), use blue tape to stick the wire bundle to the top spoke or blade. Move the wire bundle in toward the axle, or out toward the rim. When the wheel's balanced, it will come to a stop in any orientation, more or less. That's the situation described in the picture. Striving for perfection is unnecessary.

If the wire coil, moved out to the rim, isn't heavy enough to balance the wheel, use it anyway. Wrap it permanently around the rim's light spot and a nearby spoke. Start by bending over one end to make a hook that will catch on a spoke. Wrap the wire around the rim. Finally, bend the wire end into the rim or around the spoke so that it's not sticking out. Now start balancing again with another length of wire.

When the wheel balances, more or less, measure from the wheel axle to the middle of the coil and cut the wire to that length. Wrap it around the rim and a nearby spoke.

Step 29: Make the Drive Belt


One pair sheer panty-hose.

10 ft. soft clothesline rope.

The drive belt is made of one sheer panty-hose leg and about 8 or 10 ft. of clothesline rope, tied together with fisherman's knots. Why clothesline? Nylons alone are too stretchy; a strong wind can blow a belt of nylons off the drum. Use more rope than needed: temporarily tie excess rope alongside the nylon leg.
The panty-hose will supply a leg; the remainder supplies the material for a bucket filter. Tie a tight overhand knot at the top of one leg and cut the leg off just below the knot.

Join leg and clothesline with a fisherman's knot, no tighter than necessary: Tie a loose overhand knot close to an end of the rope; slip the end of the nylon leg through, and tie an overhand knot in it that encloses the first leg. Tighten the knots a little by pushing each overhand knot closer to its leg's end. Avoid pulling on a short end.

Wet the belt and give it a stretch. Tie the remaining nylon end and a portion of the rope, to make a loop around the drum and pulley. Adjust the belt length to get the lowest tension that will turn the drum.

If the belt (with some simulated playa wind) isn't turning the drum at all, lengthen it it by sliding apart the fisherman's knots. If the belt is lifting the drum's underside, it may be tighter than needed and will lift the drum fabric away from the water in the tray.

Step 30: Playa Preparations

You now have a working Gray-B-Gon evapotron, except for the plastic sheet tray liner and the bucket filter. Install those after you get to the playa.

If you have a laminated Gray-B-Gon nameplate, I hope you'll mount it on the propeller arm. It spreads the word and tells other Burners where to find this construction guide. If you don't have a nameplate, I'll mail you one.

Dismantle your Gray-B-Gon for transport in this order. Place all small parts into a ziploc bag labeled with your or your camp's name.

  • Disconnect the propeller arm from the mast by unscrewing two screws. Dismount the propeller from the arm by unscrewing two wing nuts on the angle bracket.
  • Remove the 8 wing nuts and carriage bolts that fasten the gussets to the tray. Don't unbolt the masts from their gussets.
  • To collapse the drum, turn the drum vertical, short axle piece upward, and squeeze the axle joint into alignment so the keeper pipe drops to the other end of the axle with a clack You may need to wiggle it or tap it with a hammer. Label all the parts with your or your camp's name.
  • Store the propeller and the collapsed drum in a large, clear bag to protect the blades and the tulle from damage.

Take these with you:

  • steps 28-34 of these instructions, printed and sealed in a large ziploc bag.
  • solar path lights, to protect the Gray-B-Gon from nighttime wanderers and vice versa.
  • five-gallon plastic bucket with holes in the bottom and sides.
  • one or more pairs of panty-hose with no holes above the knees.
  • polypro twine.
  • zip ties, at least 20.
  • black plastic sheet, 42" x 55" or larger; a spare sheet, or duct tape for mending, is advisable.
  • fresh 2-qt jug of Concentrated Clorox Regular Bleach. See Step 32 for info on chlorine bleach and how to apply it.
  • rag or fabric scrap, 14"x 14" or larger. This cushions the plastic sheet against abrasion by the filter bucket.
  • tools including cordless drill with phillips and drill bits, adjustable crescent wrench, and scissors.
  • eight 1-1/2" plywood staples with 1/8" holes (from step 7) and eight 1" screws.

Before you head out
The 5-gallon bucket will house the panty-hose filter for incoming graywater. Drill a few 3/8" holes in the bottom. Also drill two holes on opposite sides, halfway up. Study and practice the lark's head noose , which you'll use on the playa to fasten panty-hose to your bucket.

Depending on what's in your graywater, the panty-hose might clog up eventually. We've never encountered such a clog, but taking a spare pair wouldn't hurt.

Step 31: On Playa: Choose Location and Reassemble With Plastic Liner

Summary: Survey for wind, insert bolts in tray, place plastic liner in tray, mount masts and staples on tray.

Evaporation performance depends on your breeze. If possible avoid large trucks or structures. Negotiate with neighbors; maybe offer to help with their graywater.
Push the gusset carriage bolts through tray sides from the inside of the tray. Twist the bolts to align the square shanks with the square holes in the tray sides.

Use care not to damage the plastic sheet -- it has to hold water. Resist the urge to lay sharp tools on it. But if you do spring a leak, duct tape on dry well-cleaned plastic sheet produces a near-permanent patch.

Place the sheet in the tray floor, with weights (four food cans, for instance) holding it down in the corners. Adjust the position so the sheet lies against the floor, the rim's inside faces, and the rim tops. Don't worry yet about the sheet bunching up in the corners. If it overlaps any projecting carriage bolts, force the bolts to make holes in it.

Lay the bucket protector fabric on the floor and rim, as shown. Fasten the liner and the fabric to the rim with four of the 1-1/2" plywood staples, in the positions shown in the picture. Hold each plywood square down firmly with one hand as you start screwing, to keep the sheet from twisting up around the screw.

Reinstall the power and idler masts, capturing the liner edge under the masts and gussets.

Press a finger into one of the tray corners. With the other hand, grasp the corner of the sheet and pull upward and slightly inward. The sheet will form a fold in a straight line diagonally down to your finger. Pull the sheet corner diagonally outward and down over the rim corner. Screw a staple down over the corner. Repeat on the other three corners.

Step 32: On Playa: Re-erect the Drum

A friend is a help here. Set up the drum apart from the tray. Reaching through the gap in the tulle, place the square-cut end of the long axle piece over the far wheel's hub, and slide the keeper (3-1/2" piece of 1" pipe) inside it. Place the square-cut end of the short axle piece over the near wheel hub, align the beveled ends, and wiggle the two pipes into alignment, using your hand to hold them together. If the bracing or lacing twine is tight, you may need a screwdriver or other prying tool to align the ends. Turn the drum vertical and squeeze the junction until the keeper slides to the other end of the drum axle with an audible clack. The sideways force from the beveled ends immobilizes the keeper, so the drum is now erect and stable.

Place the drive belt around the drum. Loosen four wing nuts and tug the gusset outward, mount the drum, and tighten the wing nuts.

Step 33: On Playa: Install the Water Filter

The five-gallon plastic bucket with holes will house the water filter. Set the bucket on the fabric scrap, which protects the plastic sheet. To tether the bucket against wind, pass twine through both halfway-up holes and anchor the ends to one corner staple and one side staple.

Examine the panty-hose for holes, and tie a knot above any holes in the legs or feet. Turn the panty-hose inside out. (You may find, as I do, that looking down at the inside of panty-hose is disturbing. It's surprising what a difference reversing it makes.)

Stretch the waist over the bucket rim, and tie it in place with twine. A good knot to use is the lark's head noose ( ) It requires about 8 ft of twine. Be sure to "lock" it by adding a shoelace knot. If you need to adjust or replace the panty-hose, pull out the shoelace knot and slide the lark's head sideways to loosen it.

A sand filter is often used when processing graywater for reuse.  But we just want to get rid of it, starting by removing the chunks.  A fine mesh filter does this well -- playa dust doesn't clog it, and it's much easier to transport.

Step 34: In Operation: Disinfect With Chlorine Bleach.

Graywater is inherently unsanitary. It may contain bacteria, fungi, viruses, or other life. To disinfect graywater, and avoid funky aromas, mix in Concentrated Clorox Regular Bleach periodically.  For some antibiotic-resistant pathogens, chlorine bleach is the only reliable killer.

The active ingredient in chlorine bleach is sodium hypochlorite. It's a powerful disinfectant that self-decomposes into water and salt. Age, sunlight, warmth, and graywater impurities (including playa dust) all increase the rate of decomposition, and eventually exhaust the disinfecting power. So, make sure your bleach is newly purchased, not left over from last year. The following rule of thumb will help compensate for other uncertainties.

The No-measure Rule of Thumb for Disinfecting: Follow Your Nose

Loosen the cap of your bleach jug one-half turn: no farther, or it may come off. While using your thumb to restrain the cap, invert the jug over the tray, or over your container of incoming graywater, and dribble for about two seconds per gallon.  In half an hour or so, sniff the tray. If it doesn't have a faint chlorine aroma, dribble more bleach into the tray, about five seconds' worth.  Check the aroma again, in another half hour. Repeat as needed; morning and evening at least.

Graywater left to stand untreated eventually becomes blackwater as microbial populations increase. People who haul out all their graywater at the end of the week have worse stuff to manage than you do, unless they also treat it periodically with bleach. They also have containers that can't be reused safely for anything else.

When buying chlorine bleach, check the label for the concentration of sodium hypochlorite. Concentrated Clorox Regular Bleach has about 9%; If another brand has 6%, it should cost two-thirds as much and you'll need to add 1.5 times as much. Scented products are always lower in hypochlorite. Bleach has a limited shelf life, and this year's leftover jug won't last til next year.

Disclaimer: I am not an expert, but I have corresponded with an expert at Clorox Corp. Following the guidelines above is not guaranteed to fully disinfect your water.  I will update this step as I gain new information.

Step 35: In Operation: High Winds

High wind will blow water from the drum in droplets and distribute it downwind for several feet.  This isn't completely undesirable -- the BLM considers it to be an appropriate dispersal of treated water, as long as no muddy patch forms.

It may be undesirable, however, if neighbors are camping downwind or if foot traffic passes close to the evapotron (most of the scattered water lands close, and a muddy patch can form.) 

Some suggestions are: 
  • Lift the drive belt off the pulley wheel until the wind dies down.
  • Erect a low barrier on the upwind side, sheltering the drum.  Scrap plywood or cardboard is good.
  • Move the evapotron to a less congested location.
  • Keep the tray chlorinated, so the water doesn't smell funky and so it's evident that it's been treated.

Step 36: In Operation: Shutting Down

So it's Monday after the Temple burn, and you're packing up.  Your Gray-B-Gon evapotron, having chewed through fifty to a hundred gallons of wastewater, may now be dry, with delicate mudcrack resting on the black plastic sheet.

Or it may not.  Other camps, packing up, may still be contributing their final dishwater.  Not a problem: the dismantling process gets rid of the water.  You may want to wear rubber gloves.
  • Remove the nut or skewer that holds the propeller to its metal angle.  Unscrew the propeller arm from the mast.
  • Remove the wing nuts holding the gussets to the tray, and remove the masts and drum.
  • Remove one plywood staple anchoring the filter bucket, and remove the filter bucket.
  • Drag the tray to a nearby vacant area and, while you continue dragging, lift one end slowly.  As long as the spillage trickle you leave behind you doesn't form a mud patch, it's legal; it has been treated and dispersed.  When only mud remains in the tray, drag it back to camp.
  • Remove the rest of the plywood staples.  Lift the black plastic liner by its corners and drop it and the towel into your garbage bag or bucket.
  • Remove eight carriage bolts.
  • If you trapped the keeper with a small screw, remove it.  Turn the drum vertical and squeeze the beveled junction so the keeper slides to the other end of the axle. Remove the short and long axle pieces. Put the collapsed drum and the propeller into the large clear plastic bag for travel.
Once you get home, spray clean all the pieces.  Spray into the wheel bearings -- clean water is better for them than salty alkaline dust.  The drive belt cleans up well in a washing machine; ditto the panty-hose filter, but replace it if you prefer.  Giving the wood an annual coat of varnish, at least all the end grain and plywood edges, will greatly extend its lifetime.