Best upgrade so far
When I bought
Horizon's End there was only an overboard discharge. After buying a new holding tank and refurbishing the head, I started looking into plumbing the boat, cutting in the pump-out fittings, vent hoses, sanitation hoses, etc. That was looking like a LOT of work and $$ for the occasional weekender.
So ... I bought a portable. The 975 MSD Portable/Permanent Toilet to be exact.
It has a 5 gal holding tank, pressurized push button flush and best of all ... it's mountable - no sloshing and banging around and you can take care of business with the boat heeled over.
When it's time to empty, I take it off the boat to a nearby port-a-john (though any toilet will do) give it a rinse and we're back in action.