Looking at the plumbing for the heads on my new to me 1995 Post 46II. Looks as if the heads can be set to either flush to the holding tank OR to flush directly through the bottom. Doesn't seem likely, but that is what it looks like. As low in the boat as this plumbing is, what would prevent water from backing into (and possibly overflow) the toilets? In addition, the same area of plumbing in the forward bilge seems to have plumbing that will allow the heads to operate on either raw water fill or fresh water fill. Can any of you other Post 46 II owners confirm or correct my observations?