I have always ignored the mechanics of how the tank gets emptied. Just open deck plate and insert pump-out nozzle, or turn on macerator and let it pump, assume it works fine What i am curious about is the piping, or lack thereof inside the tank. The fittings for both the deck pump-out and the macerator (I have one of each on the tank) are on the top of the tank. Is there an interior pipe that reaches down towards the bottom of the tank to pick up the lower levels off luid, or is it emptied just with pure suction applied at the top opening? Inquiring minds finally want to know.