Return Pump Question

[molotov]

So I've just hooked up my Reeflo return pump and I'm having a bit of a problem controlling water volumes. Here are some system details:

Beananimal overflow
reeflo Dart return
Hole drilled in sump to keep reeflo flooded always

My problem is when I start to dial in my beananimal, the return pump sucks all the water out of the chamber of the sump that feeds the return pump. I can dial back the return pump but when I start to tune the beananimal the return pump sucks all the water out of the sump return chamber.

Not sure what I'm doing wrong.