I had a 10g fuge above my last tank. It was fed by a powerhead in the tank (actually tee'd off a closed loop pump) and drained back into the display.
I had a couple baffles because I was originally going to hang my skimmer on the fuge to reduce microbubbles in the display, but I would omit the baffles if I did it again. Just have a bulkhead draining to the tank (with an external durso if you like).
In the picture, the feed line goes up the right side and over the top, and the drain comes out the bulkhead in the right side of the tank.