I have a vacu flush that flushes the effluent from the toilet to the tank, but I also have the 2 switch macerator. I believe the macerator is to suck up what's in the black water holding tank, grind it up, and shoot it overboard. That's not legal anywhere in US waters to my knowledge, so I've never used it. My marina has a free pump out - that's how I empty the tank.
2003 3300 SE