REALLY COOL!!!

[muck]

For a closed loop you would need a seperate pump.
The pump pulls the water out of the tank where ever you put the intake line and puts it back into the tank where ever you put the return line(s).
There is no worry of it overflowing your sump because it doesn't go there.

Tank -> Pump -> Back to Tank

Its a great way to get more flow in your tank without having all sorts of powerheads to clutter it up. You can also drill the bottom of your tank and hide the return line(s) among rock piles or whatnot.

HTH