I need some plumbing help. I am going to run a closed loop on my new to me 180, because the tank is drilled for it and I don’t want wave makers in the display. I am assuming that the hole in the back is the outlet to the closed loop pump and the 4 returns will come over the back of the tank. I just don’t know what the two extra holes at the bottom are for. Returns from the sump? Also is anyone else running a closed loop and or Ocean Motion 4way?