The 2 barrels in this picture are hooked together with a plastic pipe, so that as the 1 barrel with the pipe from the roof fills, it overflows into the other.
We have faucets in the bottom to hook up a hose, and let gravity do its thing. I water about once a week, I fill the jugs 1 or 2 times, and run the hose underneath
the plastic to get the entire area wet. Generally each plant gets 1 gallon per week. The plastic holds the moisture in and stops weeds from growing. I do poke holes in the plastic to let rain water in.
I use a raise bed with the top edge of the dirt higher than the rest of the bed so that the water won't run off the bed into the path way. The pathways are lined with old carpet-- it holds down
the plastic, keeps my feet clean, lets water in and stops weeds from growing.
Most of my rain barrels are not hooked together. I have a 50 gallon drum under each downspout. Then there are 4 or 5 standing next to each downspout. I have a small $79 portable
sump pump I use for pumping the water out of the collection barrel into the other ones. For watering- I use the sump pump and a long hose to pump the water to the garden. Sometimes
I will get it started, then unplug the pump and let is siphon out (it is a slower stream).
Diane