I'm going to drill my tank for a 1 1/2" bulkhead. This will be on the top back with an air gap to help flow and noise. Then I'm running it to a sump (probably about 10 gallons) where it will be returned to a scwd to alternate current. What I need to know is what size mag drive should I get for return. I want max flow, but want my bulkhead to hand the flow. What do you guys think?