Introduction: Vertical Windmill Evapotron

Evapotrons are devices that get rid of graywater by evaporating it. They are mostly used at Burning Man.

My goal was to create an Evapotron that is effective, light-weight, and independent of wind direction. Upon reading the website, I read the part where it says:

Mike Robertson built this Gray-B-Gon variant:

He says,

"This is my 2010 Burning Man Greywater Evaporation Pond Windmill that I built solely from parts found at OSH. Worked great! Inspiration came from the Gray-B-Gon. As for the evaporation rate, I didn’t really measure it. It did pretty well for two peoples worth of showering for nine days though and I think if it had been a little more windy this last year it would have done a lot better.

"The bearings I used were 1 3/8” bearings and 5/8” all-thread and 5/8” collars to attach the sprockets to as well as the rotating netting and blades. The blades were made by cutting 4” PVC in half and attaching to the all-thread with 1” PVC pipe and four way fittings. Sprockets were a 42 tooth off a kid’s bike and an 11 tooth I bought off a scooter shop (make sure the sprockets are for the same type chain though). Rotating barrel is made from 1” PVC with netting draped around it. To hold it all together I use self-tapping metal screws so I could take it apart and store it."

I really like Mr. Robertson’s idea as it fits my goals. I watched the video numerous times and came up with my own way of doing things (“many ways to skin a cat”).

Step 1: Materials

Wet drum

- 2 bicycle wheels (junk yard/craigslist). Try to find wheels with a ½” bore. Otherwise, 3/8” bore works.

- 3’ all thread rod (Home Depot). Either ½” or 3/8”, depending on the size of the bicycle wheel hub.

- 6 nuts, washers, and compression washers sets (Home Depot). Star washers work best.

- 2 bearings (JSB Great Bearings). The outer diameter should be 32mm, and the bore diameter should be either 12.7mm if you are using ½” rod (part #6201-8-2RS-V1) or 10mm if you are using 3/8” rod.

- Tulle (enough to go around the drum twice)

- Sewing elastic (enough to go around each wheel)

PVC Frame (Home Depot)

- 20 feet x 1” PVC.

- 13 x 1” T connectors.

- 8 x 1” 90 degrees elbows.

- PVC cement.

- Self-tapping screws.


- 2 x 4” by 2’ ABS pipe.

- 8 x 10” sections of 1” PVC (the length of the PVC will determine how big your “fan” is).

- 8 x bolts, nuts, and star compression washers sets (for “fan”).

- 4’x ½” all thread rod.

- 4 x 1” PVC cross connectors.

- 4 x 1/2” nuts, washers, and compression washers sets.

- 2 bearings (JSB Great Bearings). OD = 32mm, bore = 12.7mm (part #6201-8-2RS-V1).


- 16” kid’s bike chain sprockets (front and back).

- Washers big enough to keep the sprockets secured and centered to the rods.

- 4 x nuts, washers, and star compression washers sets (2 sets for wet drum rod, 2 sets for windmill rod).


- 10 to 15 feet x 4” PVC pipe (enough to fit the Evapotron inside)

- Rope

- Black pond liner


- Rope

- 2 x ground stakes

Step 2: Wet Drum

Wet Drum

Start with the wet drum. Mine measures 2” by 26” (diameter of the wheels). Leave about 6”of the all-thread in on end of the wet drum.

NOTE: You can make the drum shorter or longer, but keep in mind the size of the tulle in order to determine that. The tulle must hang about 2 inches on each side of the wet drum (more on that later).

Install one bearing ½” from the end of the rod (6” section side), locking it in place with compression washers. Make sure the bearing functions properly.

Slide the bearing inside a T connector until it stops, then, without removing the T, adjust the nuts holding the drum. Bring the drum as close as possible to the T (they can’t touch). Lock all compression washers (both wheels).

Do the same thing on the other side, first installing the second bearing about 2” away from the drum, then inserting it into a cross connector until it hits the pipe reduction, then adjusting the nuts to move it closer to the drum. DO NOT adjust the drum position… you are adjusting the bearing position here. Lock all compression washers once you get the desired position.

The bearings lock the drum in place while allowing it to rotate.

Make 2 elastic loops large enough to fit the bike wheels when stretched. They will hold the tulle in place.

Wrap the drum in tulle (2 layers) and secure it in place with 2 elastic loops (one on each wheel, inside the tire channel) using the extra 2” of fabric.

OPTIONAL: For extra security, before installing the tulle, pass strings/yarn from one wheel to the other.

NOTE 2: I used painters tape in order to make the bearing fit snugly inside the PVC.

Step 3: PVC Frame

PVC Frame

Construct the PVC structure. The rod and bearings will determine how long the 4 sides must be. Precision is important here. Measure thrice, cut once. It helps to know that the reduction inside the PVC fittings sits 1.125” from the edge, so consider that when cutting your pieces.

IMPORTANT: To determine the height of the PVC structure, measure the height of the center of the wet drum (center of the rod), then add ½” to that measurement. The ½” addition will provide enough clearance from the bottom of the pond. Consider the height of the elbow fittings when making the cuts.

Once all pieces have been measured and cut, put it all together around the wet drum (it won’t fit otherwise). Make sure the drum spins easily and smoothly.

Step 4: Windmill



Cut the black ABS pipes in half lengthwise.

Mark the middle (lengthwise) of those halves.

Drill screw holes 2” from the top and bottom on those marks.

Drill screw holes 1.5” from the top of the 10” PVC pipe. Try to go through the center of the circumference.

Use bolts, nuts, and compression washers to lock all PVC pipes into the back of the ABS halves.


Cut ½” diameter holes in the middle of 2 PVC crosses.

Insert a nut, compression washer, and washer (in this order) into the ½” all-thread rod (about 26 inches down).

Put the cross into the rod using the drilled holes.

Insert a washer, compression washer, and nut (in this order) all the way close to the cross.

Turn the PVC pipes from the blades 90 degrees (top and bottom in the same direction) and insert the bottom ones into the cross you just installed.

Insert a nut, compression washer, and washer (in this order) into the rod (about 4 inches down).

Put the second cross into the rod using the drilled hole.

Insert a washer, compression washer, and nut (in this order).

Insert the top PVC pipes of the blades into the second cross. Adjust the height of the bottom cross using the 2 sets of nuts and washers sandwiching it in place. The distance between the vertical centers of the crosses is equal to the distance between the holes on the ABS pipe. If you measured it right, that should be about 20” apart.

From the other side of the rod, install a bearing close to the windmill, insert the axis into the PVC cross in the frame, and lock it in place the same way you did for the wet-drum bearings.

NOTE: Make sure the blades spin freely. If they hit the PVC frame, lower the bearing on the rod. This should raise the windmill.

Once you are satisfied with the position, insert the second bearing through the bottom part of the axis (without removing the axis from the frame) and lock it in place inside the bottom cross in the frame.

Right now you should have the horizontal rod (from the wet drum) and the vertical rod (from the windmill) meeting somewhere in the middle front part of your Evapotron. If you have lots of excess, your rods will touch.

NOTE 2: Cut either/both rods just enough so they no longer touch.

NOTE 3: Remove the blades from the axis until your gear (below) is working properly.

Step 5: Gear


Now for the tricky part... the heart of this Evapotron – the gear.


Dismantle the kids’ bike and take the front and back sprockets. Use the remaining parts of the bike for other projects.

The bike I used had large bore holes in the sprockets, so I had to improvise. I took the sprockets to Home Depot and found flat washers that would fit snuggly inside the holes (or slightly bigger), while having the correct diameter themselves to fit into the axis.

Since the front sprocket had a squared shape, I used a Dremel to cut the round washer. It fits perfectly inside.

Horizontal Axis

Install a nut, compression washer, and washer into the horizontal rod.

Install the front sprocket assembly, which in my case means the sprocket and the squared washer inside of it.

Install a washer, compression washer, and nut, sandwiching the front sprocket assembly. Tighten by hand for now.

Vertical Axis

Install a nut, compression washer, and washer into the vertical rod.

Install the back sprocket assembly.

Install a washer, compression washer, and nut, sandwiching the back sprocket assembly. Tighten by hand for now.


Move the vertical sprocket high enough in the vertical rod so its teeth are at the height of the horizontal sprocket’s teeth.

Move the horizontal sprockets forward until its teeth meet the vertical sprocket’s teeth.

Tighten everything and give it a light spin.

Keep playing with these adjustments, including how centered the sprockets are fixed in the rods, until you have the golden-lock position. The gear should spin very smoothly and you should not hear any clinking (clinking means the sprockets must be further apart).

Step 6: Pond


I have 4 pieces of 4” PVC cut large enough to accommodate the Evapotron inside once assembled in a rectangle configuration.

Pass a rope through the length of all 4 pieces (long, short, long, short order), arrange the pieces in a rectangle, join the ends, make the rope taut, and tie a good knot. This will prevent the pieces from rolling apart once water is added to the pond.

Cover the PVC pipes with a pond liner large enough to tuck it under the pipes.

Step 7: Securing the Evapotron

Securing the Evapotron

Think about how you would dismantle the evapotron and put it back together at Playa. I chose to glue some parts with PVC cement and screw others using self-tapping screws for easy storage and transporting.

Once on Playa, install 2 ground stakes to the sides of the pond (around the middle area of the wet drum).

Tie a rope to one of the stakes, pass it over the PVC structure, and tie it to the other stake, making the rope taut.