and btw those round sponges go in the back of the prefilter, around the pipes the hoses the water goes down. ill find a pic for ya. heres how i prime my U tube. first remove the clear overflowbox. now take the U tube. i plug one end with a round cork bobber and submerge the tube, getting all the air out. then i leave the unplugged end in the water and slowly place the corked end into the back of the prefilter. i get someone to turn on the pump and simultaneously unplug the cork. works every time. now place the overflow box back on and ajust your sump water level.