well, then that brings up my next question.. hehehe... an overflow wall needs to be how big for a 75g tank? I had thought of cutting a piece of 6" pvc in half and match their height to the top of the tank, then cut teeth into the top of the pvc. Then place each 1/2 on the 1/3 marks of the tank. I.E.: if a tank is 48" long as this one is, they would be centered on the 16" marks coming from each side. Of course, pre-drill a hole at each of those marks as well... Or would this not be enough overflow?