I would need to see pics of the sump to be of much help, but i always use a sort of cage made out of needlepoint backing material to set my return pump in. It not only stops the bubbles, but will also keep any critters that make thier way into the sump from getting sucked into the pump and returned to the display as a hundred tiny pieces. Pods also like to hang out on the stuff, so they tend to get sucked into the display more regular.