Step 6: A variation with three barrels
I decided that, instead of having the first barrel drip into the second one, I would have each barrel flow directly into the side of the next one. The connectors are the same as before. I simply cut a 4" PVC section of pipe and slipped it into the two female smooth receivers on each barrel. If I want to disconnect, I simply pull an outer barrel away from the next one and it slides right out. There is no need to cement the pipe in. You can see the results in the two photos.
Lesson learned: These barrels seem to come with several variations in design and I wasn't aware of this until I got them home. The barrels I used in the main tutorial are squatter but the same capacity of the the two newer ones I bought. The barrel on the left is of this type. Notice that it is raised up on a wood platform. I had to do this because the two newer barrels were taller and the third one had to be raised to meet the pipe coming in from the second one. Another problem is that the two newer ones have an inward slant near the top. Drilling a 13/16th inch hole near the top would have pointed the pipe upwards instead of horizontally. I had to make the hole about 3 inches from the to make the pipe horizontal. That means that I am wasting some of the capacity. When you buy barrels for a project like this, pay attention to the design.
[update 19 June 2010] I just added another instructable involving the rain barrels at this shed: http://www.instructables.com/id/Redirect-water-from-a-raingutter-to-a-rain-barrel/
This shows how I directed water from the front gutter to the barrels in the rear using PVC piping.
This shed is the source of all kinds of experimentation. Yet another instructable shows how we added solar panels to it: http://www.instructables.com/id/How-to-mount-a-solar-panel/.