Dripper irrigation currently uses a pretty crude 'water clock" with clean water as a controller to allow water (clean dirty or recycled) to drip into a plant container at a constant rate so that it never gets completely dry. I have asked an electronics student for quotes for something to replace the waterclock but so far nothing.
Many different sorts of controllers could be used. I am just evaluating it right now to see how slow it can go while still remaining reliable. So September 14th. We are around a litre per hour of dripping so you can get about a week out of the water barrel!
I have used 3 inch pipes in mine but 2 inch might work too. (My supplier charges more for 2 inch than 3 inch pipes!).
I am using it in one of my pallet garden experiments until I get a little airlift pump organized for it.
Dripper irrigation playlist is at http://www.youtube.com/playlist?list=PLkzXlmAwZTZdjGtjJpCYm2gSGVGwA033M&feature=view_all and it has worked super so far.