For the next step I bought the following parts.
1/2 in. MNPT x Barb Adapter
1/2 in. PVC Schedule 40 FPT x FPT Ball Valve
1/2 in. PVC Schedule 40 90-Degree S x MPT Elbow
1/2 in. x 2 ft. PVC Schedule 40 Plain End Pipe
I'll take some space here to to explain the above abbreviations.
FPT = female pipe thread
MNPT = male national pipe thread
MPT = male pipe thread (same as MNPT)
S = slip connection (PVC cement is needed)
I put this here because I was quite confused by it for a while. Back when I was first putting in my rain barrels I bought several PVC fittings to connect to the barrel overflow outlets. They wouldn't go on cleanly. I could force them, but I knew something wasn't right. It turned out that the barrel had what are known as "hose threads". From what I've found, garden hoses have hose threads and pretty much everything else uses pipe threads. There are adapters to go from one to the other. You can read more about it here.
With the parts listed above I made this. I used teflon tape on the threads.
Then I put the PVC pipe through the Uniseal in the bottom of the trash can.
Next I filled the barrel. I've been saving kitchen scraps, and the pulp from the juicer in a 5-gallon bucket. Luckily it's been cold so it didn't attract bugs or rot too much. A 5-gallon bucket of kitchen waste didn't do much to fill the 55-gallon barrel. I added a wheelbarrow load of chicken manure and pine shavings from the coop. It still wasn't full, so I added half a wheelbarrow load of leaves.
Then I ran a hose from one of the rain barrels and filled the blue barrel with water.
Here it is full of water. You can see that the mess in there floated. Before the water was added it was only as high as the trash can.
Finally I installed the trash can. I had the ball valve open and slowly submerged it over the material to be composted. It took a while to get all of the air out. Once it was finally down I closed the ball valve. I placed a few chunks of concrete on top to weigh it down.
In theory, most of the oxygen should have been pressed out from under the trash can as it was submerged. The trash can should rise as the methane is produced. At that point I'll be able to collect or use it by attaching a hose or balloon to the barbed fitting and opening the valve. That's the theory anyway.
Biogas: Volumes 1 and 2
Steven Harris on Bio Fuels for Personal Energy Indepencence