Here is an example of how to build a manifold system using sprinkler valves. I have had better luck and fewer issues with the single pump and sprinkler valve system. I will be creating a new thread in about two weeks of my GIII upgrade to SUPER GIII system. I have built two systems, one with individual pumps and no manifolds and one with a HUGE single pump and sprinkler manifolds. The sprinkler manifold performed way better than the individual pumps and I did not have to use vented loops, plus I tested my system with all of the hoses hooked up full length on both systems and the sprinkler manifold system was almost a third faster!!! So don't let people tell you the sprinkler valves are ALWAYS slower. I will be debuting one shortly that is super simple and is faster than individual pumps. THE ABOVE STATEMENT IS FOR CINTRIFUGAL PUMPS NOT THE NEW JABSCO PUMPS. The new system like in ED_Gs boat will smoke mine, but I did not have the cash to go that route. My comparison was done with 3 Tsunami 800s vs a Rule 3800 and sprinkler valves.

Back to the manifold, cut all of your pieces and then test fit them in the boat, mark each side of the pipes with a sharpie, remove the system and re-assemble using the proper primer and glue. Here is a sneak peak at my creation: