The best way to set up such a system would be to pumpo water from the tank to buckets ABOVE the tank...and let the water flow through it (via gravity) back into the tank. It's called a "dump" filter and works great.
I'd also suggest a mechanical filter layer as the top layer to remove crud before it gets to the bio media.
I'd also suggest a mechanical filter layer as the top layer to remove crud before it gets to the bio media.