Its surprising to me that many boats I see on Sydney harbour have the old school heads with no holding tank. I wonder where all the stuff goes? The few times we have ladies on board they never want to use the loo anyway, and I guess the boys go in the cup and then overboard. (many drowned males are found drowned with flies down)
I had the backing plates of my head thru hulls rotting out so I decided to get drastic. I ripped out the head, glassed in the thru hulls, and put in the porta potty. It was a ****ty job, but now I only have to lug the thing ashore once every blue moon. I guess I can feel smug not I have done the deed but I still wonder where all the other stuff goes?
I think Jode and South ace put me on to these composite skin fittings and sea cocks if there epoxied into the hull they become part of the hull and don't rot
www.trudesign.nz/marine/certifications/1-seacocks-and-through-hull-fittings
Have a think about the rest of the world and how they use the local rivers China and India come to mind 
It goes into the oggin. We are a fresh water animal as is our bacteria. It doesn't last long in salt water.
I've got one of those old heads in my Tophat from when I bought her. I have toyed with the idea of removing the existing heads and replacing with a portapoti.
My thought at the moment is that there is a small compartment under the forward berth that will fit a portapoti and I'm figuring I'll put one there and eventually retrofit a holding tank and macerator for the existing unit.
