You want two overflows. check out my photogallery. you can see the position of them. you can also have them in the corners. let the aquarium company set it up with their standard kits so your piping will connect without problems. you will need to size your return pump so as not to fill faster than the drain. a float switch connected to the pump could handle this problem, but by putting a valve on the return and adjusting them equal you can also manage it. Many ways to set it up, but, definitely two overflows. ask the manufacturer for an overflow kit that goes inside the overflows to return water and preclude the slup slup or perverbial water fall sound. you will need one kit for each over flow. hope this helps.