Is this tank drilled or do you intend to use a HOB
overflow? If it's drilled, gravity does the work, and the diameter of your drain will dictate the maximum you can return to the DT. If this is a HOB
setup, water is brought from the DT to the sump by siphon, and your return pump needs to match your HOB
overflow as close as possible or it can lose siphon.
You do not want to adjust anything in the sump. let the water go through at the speed it's dropping from the DT.