I created this gravity based bucket drip system to water my trees. The pressure is very low, but I found that as long as the water reservoir is a couple feet higher than the drippers, the hydraulic head is sufficient.
Pros: saves water, saves time, good for rainwater trap system.
Cons: potential of failure due to clogged lines or dead batteries, have to monitor/refill water in reservoir, cost of components.
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30 gallon reservoir.
I'm using a Rain Drip timer that has very simple twist-knob controls.
1/4" plastic irrigation hose line.
About 10 Rain Drip in-line 1/2 gph drippers per tree (would be 5gph per tree at normal/garden hose water pressure).
I switched to 1/4" soaker hose made bendable with a wire in the center for more even distribution. I poked holes in it to increase flow where needed.
Upgraded to a 45 gallon reservoir.
Went back to the in-line drippers after discovering that the soaker hose tends to clog easily and does not provide a consistent drip. I went w/ two rings to provide even distribution and it seems to be working great so far.