Originally Posted by Reefer27
I don't see the need for a drilled return line. I don't mind piping over the back of the tank. Plus this way there is no siphoning chance. ( I know not much would siphon back).
If your return line is underwater, no matter if it's over the top or thru a hole, the water will siphon back into the sump until the water level in the tank drops below the level of the return. You can go over the back, but if you take the return line to the bottom of the tank, when the pump is off the entire tank will drain. If it's 4" deep, it will drain 4" of water.
You can take the return all the way to the bottom or as deep as you want, IF you drill a small hole in the return line near the surface (1-2" deep), so when the water drops it will break the siphon. Basically, it doesn't matter if it's drilled or over the top if you set it up correctly to break the siphon before the sump floods.