Some do use a ziploc, or a garbage bag, or whatever for all the paper esp when using the head in shallow confined coves, parks and marinas. It takes some getting used to.
It also makes it even more important to be able to find regular means of garbage disposal ashore....
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)