Hi all. I recently was gifted an acrylic aquarium that I'm hoping to set up as a reef tank. The aquarium has dual overflows (one in each corner), but inside each of the overflows there is only one single hole at the bottom of the tank w/ a 2" diameter. I'm used to seeing two holes inside each overflow. Why is there only a single hole in each overflow? Also there is an additional hole (hole #3) on the bottom of the tank located in the middle of the tank towards the back wall. This third hole is currently plugged, but there is no overflow/box hiding it so its just kind of in the middle of the tank. Does anyone have any clue on how this tank is supposed to be plumbed?