I have to throttle back my return pump (a Mag 7.5) because the two built-in drains are only 1". I thought of using a HOB overflow along w/ the built-ins, and then I could open the return pump all the way. But, I don't want to have the overflow box inside the tank.

Is there a problem using one of the existing built-in overflow's inside part, along with a U-tube and an outside part of an overflow to accomplish what I want?

(Does this even make sense? I know what I'm thinking. I just don't know if I'm saying it right.)