Here's an old powercruiser trick:
Use a porta potty, attach a fitting and hose to the tank portion. the 1" hose goes to a macerator pump. The porta potty is legal
as it has a holding tank. The macerator goes to a thru hull
valve that is closed in protected waters. simple easy . I seen many of them on small power cruisers.
Another advantage is there are no internal head parts
to fail or clog. You just have to worry about the macerator. You could put a diaphragm
manual pump in place of the macerator.