Previous boat was a Hunter 23.5 with a portapottie. Just purchased a 2001 Hunter 290 with a marine head. Pumped out the new boat for the first time and the tank gauge continues to read full. Pumped out until it was only drawing the raw water I was pulling into the system. Ran fresh water into the tank and pumped it out too. Is it possible the float (if it has one) is stuck? If so, is there some way to free it? What other avenues should I pursue to remedy the problem? The head seems to work well otherwise.Thanks