You are correct just the caps have holes drilled in them. Before I filled the tank I ran water up from the sump and tried different sizes and numbers of holes in each cap to try and get a fairly even amount from each cap. The three at the far end got a little more flow. I have an inline one way valve and I also drilled a hole to break the siphon. As an added bonus the siphon hole makes some nice surface agitation.Baxreefs said:The "under sand" return is an interesting idea. I assume that there are holes only in the very end of the piping above the sand?
Just be sure to drill a 1/8" hole as a siphon break in the return line about 1" below the normal water line in the tank. Other wise it can siphon water and sand back to the sump and cause a real mess ... not that anything like that has ever happened to me :