[Mah na' Mah na']

1999 40 express: has anyone had a problem with the sea locker (gray water holding tank located center aft in the engine room) not working? My switch seems to be telling the pump to run when there is water in the tank, and the pump runs but nothing is coming out. As a result, the pump runs all the time but not pumping anything. The pump is accessed via the hatch in the floor of the transom storage garage but way back under to port and very hard to get to. Has anyone tried to replace this before?? Looking for any guidence on this. Do I do it myself, or save myself the busted knuckles, sore back, and bruised ego and hire it done.