This is about boat bathrooms, so you perverts can go back to other threads now.

If a boat has a pump out porta potty, does that mean it pumps directly out of the tank on the bottom of the porta potty? Or is there typically some sort of holding tank?

Vacu-flush heads I assume always have a holding tank of some sort.

Anyone ever covert a boat from one to the other?

your right. the porta potties with pump out feature pump right out of the potties tank, no seperate tank. Vacu flush has a holding tank. Vacu-flush is expensive. I installed an electric head on mine that chews eveything up and sends it to the holding tank in a 1" hose. Easy, not too expensive and the girls like it cause all you have to do is push a button, no valves to position, no handles, pumps. just real easy. I also use my fresh water system instead of raw water. Keeps it a alot fresher.