An overhead or "dump" filter is the way to go: Basically a pump in the tank pushes water to a container on top of the tank and the water "dumps" back into the tank via gravity.
I have them on most of my large tanks. An actual sump, a rubbermaid bin, a decorative planter or just about anything that holds water can work.
This tank is going in my living room and one in my family room (new addition) an overhead sump is not going to work.
