[RickT]

Re: Vacuflush Discharge pumps - You will know when the tank is empty when you see and hear bubbles coming from the underwater discharge. You can't miss it. Good thing they added an on and off switch to the thru hull since operating the pump with the thru hull closed implodes the duck bills in the pump. I just replaced mine on a 2001 3500 Express. The duck bills were trashed impressively. One imploded into itself the other exploded impressively out such that you would never guess it was ever a duck bill. These are impressive pumps, very robust, unlike the less expensive Jabsco's you get to replace every two to ten years or so.