heres pics of the overflow the right pic shows a side view and the left pic is a top view. top view right you can see where i had to silicone from the pacu thrashing, and on the left you can see where i had to silicone a air line tubing to suck out the air in the top of the overflow box to keep the siphon going. the airline hooks to a pump. as for flow rate the pump has no brand name, it is from a pond kit at walmart, the specs are 600 gallons an hour.