Mike the combinations are endless. My system drains a gravel bed into a raft and a siphon drains out the other end. I did this to create a toilet effect instead of a overflow off of the side to add more air to the water column. It then drains to the fish tank which is buried at ground level. Other Ideas is put the pump in the raft and pump to the fish and let gravity push the water through the filter and drop to the raft at the opposite end. Just remember you have to filter the water somehow and there is alot more experts than me on how to do this. I chose a low tech approach instead of a swirl filter and clarifier.