My masorator pump quit working so I called the company and they said not to run it dry so I replaced the impeller (it was chewed up) and put a on/off switch right by the masorator pump that way when I open the black tank valve I can run the masorator pump and shut if off after the gray in empty.

The way mine was set up the switch was at the dash and when the pump was done pumping, I went to the dash and shut it off.