The overflows have a box built around them. The water overflows at the top of this bix, and down the overflow to the sump, and fuge. I have a hole drilled in the sump, where the intake of the return pump attaches. The water pump sucks the water from the sump into the intake, and pushes it up the return line. The return line goes into the tank, and the water exits from the return into the tank.