It has its own pump?
You sure? Those usually work off of gravity, where the water creates a siphon that pulls water down into your sump. What causes a siphon to break is air. If air is introduced into the siphon and isn't cleared out, it will break your siphon potently causing your tank to overflow.
U-tubes can also gather air pockets, but in my experience it is very not-often, especially if you have two u-tubes in one overflow for redundancy.
, in a traditional sump/overflow box setup, the only pump that is needed is a return pump that can pump LESS than the overflow box can drain. No 2nd pump is needed to bring water down from your tank to your sump. (a pump for a skimmer might also be there, but again, that's a part of the skimmer assembly, not your general sump).