The 2 tees you see on the back wall are the intakes for the closed loop pump they return through an oceansmotions 4 way and 8 revolutions. 3 down each side, 1 top center of tank, and 1 bottom center of tank. The 2 returns at the top work great, they gravity feed my skimmer and go to my sump. This pic was taken before it was stocked with corals. I am growning the tank from frags except 1 or 2 small colonies.