I love this idea and would love to build one soon (ie. this fall), I need to start and finish the barrel washer first. I have two ideas I would like to add.
1) have the drip tape snake through a bucket of bleachy/vinagery water to help disinfect it.
2) add a measuring wheel so that you can mark how long each piece is....they get shorter and shorter with time because of holes and couplers http://www.amazon.com/Walking-wheel-Tape-telescoping-handle/dp/B0002JKBHG/ref=sr_1_4?ie=UTF8&qid=1375704313&sr=8-4&keywords=wheel+measure