This is a cistern I made from some pressure treated 2x6 material and a 55 gallon plastic juice drum. I got the used drum locally for $15 and the wood came from my scrap bin. I chose to use 2x6 material because I had it handy, but if you choose to use 2x4 instead, some dimensions will change. I haven't done any structural calcs, but the water weight alone of 55 gallons of rain will be about 459 pounds, so keep that in mind if you change the size. I use this to water my vegetable garden which is nice and close to the cistern.

To make this, you will need:

Aa 55 gallon plastic drum with the screw caps intact
The following pieces of 2x6 pressure treated (PT) lumber:
- (4) 28.5"
- (7) 24"
- (4) 23"
- (4) 18"
- (2) 13"
Construction adhesive
2-1/2" all purpose fasteners
(3) 2" PVC 90 degree elbows
Small lengths of 2" PVC
3" to 2" PVC reducing bushing (to attach to your gutter's downspout - your application may vary)
(1) 3/4" PVC threaded male adapter (to attach to the barrel's cap)
(1) 3/4" PVC 90 degree elbow
(1) 3/4" PVC shut-off valve (controls the flow of the rainwater when you use it!)
(1) 3/4" slip x 3/4" MHT PVC fittings (this is at the end of the pipe exiting the barrel - you can attach your garden hose to this)
(1) 2" PVC coupling (this will form a riser to keep sediment out of your garden water)
(1) 2" PVC male adapter
(1) 2" PVC female adapter
Epoxy

Step 1: Get a Leg Up

Start by glueing and screwing 2 lengths of 2x6 together, keeping the bottom end flush. They are 28.5" and 23" long, respectively.

Step 2: Two Legs Are Better Than One

Repeat step 1 to make a built-up second leg.

Step 3: A Time to Join

Next, cut an 18" piece of 2x6 and glue & screw it between 2 of the legs.

Step 4: Have a Pair

Now repeat steps 1-3 so you have an identical U-shaped assembly.

Step 5: Come Together

Now, cut a 24" piece of 2x6, and slap some adhesive on the 'notches' at the top ends of the 2 leg assemblies. Place the 24" 2x6 and screw it in.

Step 6: Deja Vu

Repeat step 5 for the other side.

Step 7: Sister Marry Me Please

The next thing is to sister up the 4 leg stretchers to beef them up a bit. For this, you will need two 18" and two 13" pieces of 2x6. Glue and screw them in place.

Step 8: Top It Off

The last part of the stand construction is to make the top. Just use whatever 2x material you have, cut them to 24" length and space them evenly. You could make an overhang if you wish, but I preferred the cleaner look of making it flush. Remember to put a space between boards to give rainwater a place to drain.

Step 9: Down the Drain

The next step is to prepare the stand for the barrel's drain. This requires drilling a hole in the top, and another in the side. There will be a 3/4" PVC pipe that exits the barrel, and turns 90 degrees to protrude out of the stand's side. I chose a 1-1/2" drill bit for the hole on the top (to allow a little bit of wiggle room), and a smaller one for the hole in the front.

With the 2 holes drilled, next you must attach the PVC to the drum's screw on cap. However, to keep sediment from entering the drain, I added a riser to the inside of the cap. The riser is nothing more than a 2" PVC coupling. I mixed up some epoxy, poured it in the recess and stuck the coupling on. For my drum, the cap is outfitted with a threaded hole that fit a 3/4" threaded male coupling perfectly.

Now it is time to assemble the 3/4" PVC components that make up the rest of the drain. Note that some of them need to be assembled once the barrel is in it's final resting place. See the 'exploded view' for a complete visual of which pieces go where. Basically, the vertical parts can be assemled/attached, then you place the barrel on the stand, then you assemble/attach the horizontal parts.

Step 10: A Solid Foundation

With the drain pipe installed on the barrel, now you must pick a spot for the barrel and prepare the foundation. For me, it was directly under the gutter's downspout. The foundation itself is nothing more than 4 chunks of pressure treated 4x6 wood, placed on level ground. Cinder blocks would work too - the main idea is to spread out the weight of the full barrel.

Step 11: Connect to Gutter

Next the rainwater needs to be diverted into the barrel. Your application may differ, but the basic premise is to pipe the water into a hole cut in the top of the barrel. For me, a 3" to 2" PVC reducer fit perfectly onto the gutter's flange (attached with sheet metal screws). I came out of the reducer with a 2" PVC elbow, then another, then a 6" length of 2" PVC, directly into the barrel.

Step 12: Overflow Mechanism

When the barrel is full, you will want additional rainwater to take it's normal course through the downspout. To achieve this, I used the male and female 2" PVC adapters, a 2" PVC elbow, and a short piece of 2" PVC. Cut a round hole in the side of the barrel at the elevation you want to be the high water mark. Make the hole sized so the male adapter will fit snug. Pass the male adapter through, and screw on the female adapter. Now you have a PVC fitting on which to glue the elbow (on the outside), then a short piece of 2" PVC which sticks into the downspout.