Since the rain barrel post seemed to spark some interest, and it’s a relatively easy do-it-yourself job, we thought we’d post a tutorial. So here goes:
First, obtain all needed materials, most importantly, a large barrel (or several of them). Probably the easiest thing to get your hands on will be a 55 gallon drum from a nearby farmer. If the farmer is nice (which most are), they’ll even cut off the top of the barrel for you. I obtained all three of my 55 gallon drums and the big 330 gallon tank from farmers and people who live out in the country. However, I also see them for sale on craigslist occasionally; so if you live in the city, chances are someone in the metro area is trying to get rid of some big barrels. Your final option is to buy a pre-made rain barrel from some big box like Menards or Fleet Farm, in which case, you can stop reading now and go shopping.
Once you have your barrel, gather the other tools and materials. You’ll want a drill and a spade bit for drilling the hole; a hose faucet valve with two washers and a nut; and some silicone for caulking around the valve. My bit was 7/8, which drilled a hole just big enough for the faucet to stick through. If you’re confused at this point, just stare blankly in the middle of the hardware aisle until an attendant asks you if you’re feeling okay. Nod, “yes” then explain that you are making a rain barrel and need the necessary parts. 
If possible, pull out your smartphone and show the attendant the picture from this post and have her find the equivalent parts. This is, in fact, the most difficult part of this project — navigating the intensely confusing hardware store aisles looking for something other than spray paint. Make sure the washers and nut fit perfectly around the threaded part of the faucet piece.
Anyway, hopefully at some point you make it back home with the things you need, and can begin the fun part. Hook up that bit to your drill and position it a few inches from the bottom of the barrel. Don’t worry about needing to fit a bucket under the faucet because you will want to elevate the barrel off the ground on blocks or stumps once you are finished. Now, go ahead and drill your hole.
Great, now take the faucet, the washers, and the nut, and prepare to fasten the faucet to the barrel. The first thing you should do is press a ring of silicone around each washer and set one of them aside. Position the other washer over the hole you just drilled, and then take the faucet and stick it through the washer and hole. 
You’ll then want to press another bead of silicone in the seam between the washer and barrel, and another bead between the faucet and washer. Basically, you’re going to caulk with silicone wherever there is a seam between parts.
Fantastic, now, lay your barrel on its side, being careful that the faucet stays in place, and prepare to crawl inside the barrel with the other washer, silicone, and the nut and in order to fasten the faucet with the nut. Bead the silicone on the washer and place the washer around the part of the faucet that sticks into the barrel. Now hand-tighten the nut along the threads. Again, bead the silicone around the washer and the nut — don’t be afraid to use your finger to smooth the silicone around the seams. It also works good to have your children beat on the barrel with their popsicles, treating you to the acoustic wonders of a 55 gallon drum.
If you are not satisfied with how tight you were able to get the nut by hand, it wouldn’t hurt to get a vice grips and a wrench to finish the job. Use the vice grips to hold the nut in place on the inside of the barrel, and then get someone else to tighten the faucet from the outside using a wrench. As you tighten you may see more silicone squeeze out from the washers; again, use your finger to make a smooth ring around the pieces.
Once you are satisfied with the tightness of the faucet and nut, and you have adequately caulked the seams with silicone, you are basically done with the barrel. The silicone will need several hours to set, so don’t plan on letting water into the barrel the same day you complete the project. In the meantime, you want to make sure your gutters are in good condition and your downspouts are positioned for your barrel. You may need to cut one of your downspouts or unscrew a few joints to reposition the downspouts (but don’t stress too much about this because gutters are pretty cheap).
When you’re ready, position the barrel with the downspout running into it, and set the barrel up on blocks or stumps. This allows you to fit buckets underneath the faucet, and it raises the faucet so that gravity will work with you, forcing water through your hose when the barrel fills up. It’s a pretty nifty deal. Lastly, you may want to find a board or some sort of screen to set across the top of the barrel to keep critters from climbing into the water and drowning. And be sure to not let young kids climb on the barrels or hang over the edge.
Enjoy your project and happy gardening!
He Sowed She Sewed 