i made my return on them outa pvc, and placed this at the end, and kept hte center piece in halfway.
another option, that always works is panty hoses, i acutally run 2 layers of panyt hoses on my return, it prevents alot of stuff from gettin sucked up, and prevents any kind of bubbles from coming outa the return. so place panty hose where it comes out.
either way, one of those might be able to fix your problem