If your tank is undrilled you'll need to pick up an HOT style over flow box. Visit any online supply and the sell them. You'll get the idea when you see it. You'll need a suitable return pump to lift the water back to the tank. I prefer Eheim. Look at picking up something in the 5-10 times the volume of the tank for the return flow. As in, 100g tank 700-1,000GPH pump.