Cool web page. I didnt read the above comments, but heres mine:
why not keep it simple and have one Green line up to the top tank, a couple of grey connections between the other tanks, and one red return back to the sump?
do you need to have 2 lines from the sump pump?
i guess for this to work the parallel grey lines would have to flow down, so each tank would have to be slightly higher than the other.
youre right, PVC is cheap, so you can just buy a bunch of straights, turns, and connections and dry fit it until you get something that works. dont glue until youre sure. then do a wet run with tap water before fillign the tank with good water.
use a union fitting from the sump pump so that its easy to disconnect for cleaning purposes. in fact, while they cost a bit more, unions are good to use in other areas so you can quick disconnect whenever needed.
good luck!
EDIT: after reading the above comments on the plywood shelves you might want to thnk it out first. if you say one gallon of water = 7 or 8 pounds. then add in the rock and other equipment. you might want to check if a piece of pywood can handle that type of horizontal compression. a piece of 2x4, on the other hand, compressed vertically, can hold a tremendous amount of weight. also, if the wood bows but doesnt break, that can be just as bad, as uneven support on the bottom of your tank can cause the tank to break! and, finally, you want it to be as level as possible. this is more critical for larger tanks, but nonetheless. an unlevel tank can also cause a break. so, if you use the cinderblocks, make sure the surface is level! hope that helps!!!
