Find Your Barrel
Some people use beautiful oak barrels for their rain barrels. The look is stunning. So is the cost. You can find 55-gallon plastic barrels online for around $15. These barrels are used to transport foodstuffs like sauces and syrups. Be sure yours is food-grade.
Use the Screw-tops
Your plastic barrel is ingeniously designed with two screw-top openings. They have threaded knock-outs in the middle. Using a 7/8-inch drill bit, drill out one of the knockouts. This is where you'll attach your spigot assembly.
Turn the Barrel over and Cut an Intake Hole
Place a basket designed for water plants (available at many lawn and garden centers) upside down and trace its outline on the top of the barrel (the side with no screw-tops). Next, measure 1/4-inch inside the trace line and draw a cutting outline. You're creating a lip for your basket to sit on. Drill a starter hole, then cut along the line with a jigsaw. Make sure your basket fits easily into the hole. At this point, rinse out the inside of your barrel.
Create an Overflow
Rain barrels fill up. Using a 1-inch drill bit, drill into the side of your barrel as high as you can. Then screw in a 3/4-inch adaptor. Be sure to use plumber's tape on the thread. Attach a short piece of hose to divert the overflow away from your house.
Now for the "Plumbing"
Unscrew the screw-top you drilled and wrap plumber's tape around its big thread, then screw it back in. Now, screw in a riser (don't forget the plumber's tape) into the knock-out threading. Attach the threadless elbow joint with PVC cement (you might want to put the pieces together in a dry run first to make sure everything fits). Next, you'll want to cut enough PVC piping to extend your ball valve beyond the edge of the barrel to turn it on and off (about 4 1/2 inches, depending on your barrel). Cut another 1 1/2 inches of pipe and stick it into the other end of the ball valve. Attach the elbow with the threaded end and you're done. Just make sure everything is pointing in the right direction before you apply the PVC cement.
Create a Raised Platform
Elevating your rain barrel creates water pressure and makes it easier to put a watering can or bucket under the spigot. You can use cinder blocks, decorative paving stones, wood, or railroad ties to create a platform for your barrel. Just be sure to make it level, and place it next to a downspout.
Divert Your Downspout
You can go pay $35-$90 for diverter kit for your rain barrel. Or, for about $5, you can buy a flexible accordion-type diverter at most hardware stores. Cut a section out of your downspout with enough room for your diverter. Then extend it to the top hole in your rain barrel. Be sure to secure the top of the diverter to the downspout with a screw. You are now ready to collect rain. In the winter, just use your diverter to reconnect to the bottom part of your downspout.
The Final Touch: Painting
Unless you like industrial blue, black, or white, you can paint your barrel to suit your tastes. Use a paint that's made to adhere to plastic. You can match the color of your house, or paint it to look like terra-cotta. You'll be amazed at how good your barrel looks in its new coating.
Using Your Rainbarrel
You can attach a soaker hose to your barrel for your extra-thirsty plants. Regular hoses work, too, but without the blast of pressure you're used to. Plan on giving your watering can a good workout with your rain barrel.
Line your basket with screening and glue down the edges with strong glue. Another option is to use Mosquito Donuts, available at many lawn and garden centers. They contain bacteria that attack mosquito larvae, but are harmless to you.