Here is what is in there. Its likely the ball and
check valve are rusty and has locked the valve
shut. If you can back the cover out a half a turn
and squirt some penetrating oil in the holes on
the side you should get it to free up. Here are
a few options to back the cover out. You may
have a better idea. Best solution though is to
take it apart and clean it out.
Tubs
A "Boathouse Repair" is one thats done without having tools or the skills to do it properly.
