Originally Posted by germanyt
So the hole could be drilled 2 feet off the ground and the sump sit on the floor and it would still work properly.
I'll have to learn some more about saltwater tanks I guess.
Basically with a DT / sump setup one tank drains into the other requiring a gravity based overflow while the lower tank pumps water into the top one. It doesn't matter if the DT is the top or bottom tank but the bottom tank will have varying water levels hence my suggestion for an automatic top off. As for drilling the hole, it's usually easier to have the hole drilled in the side of the tank.
As for having a 4 - 5 ft deep tank, you would need a serious light system to get light all the way down to the bottom, even more so if you wanted a reef. Lights have a hard time with penetrating any large distance.