I used this system design without using 2 liter bottles ..I used three in sched 40 pvc instead..I tapered them down using flanges to fit into 1 inch threaded elbows and 90's......Check out rons11plant garden and you will see my hydrosetup with 12 inch peices of 3 in sched 40 pvc instead of his 2liter bottles....used as planters 3 inch netpots fit perfectly into 3 inch pvc..I kept burning the plants because i think the 12 inch airstone in the holding tank wasn't doing any good the air wasn't going to the individual planters when they where flooded I bet it would work better if I had an airstone in each planter..Goto this website and click on 11 plant garden it offers design.
http://www.hydroponicsonline.com/Store/index.html