I recently set up an Oceanic 120. I use one pump (actually two Iwaki 30 RLXT in series since it is from a basement to the first floor) that is split with a T to two returns over the back (it actually feeds other tanks as well), and I use all 4 drilled holes in the overflows to take water out of the tank (two for ordinary use, and the two smaller ones as emergency drains).