HeadMistress ansering your call to weigh in:
I've been trying to figure out the toilet and plumbing...I've never seen anything quite like it. There are no markings on any of it. No sign of a pump for the toilet. There's a long piece of hard PVC that appears to have the diameter of a discharge line but it seems to run way to0 high for a discharge and no way to see what's at the other end of it...and no sign of any flush water piping or source (I wonder if it's something called a "dry toilet"...I've heard of 'em, but never seen one). There appears to be the edge of a pedal sticking out from under the bowl but maybe not. So I don't have a clue what he has, how it supposedly works or what it drains into. However I did see that there are two deck plates on the side deck--one marked "water"--either the fresh water tank fill or the ballast tank fill--and one marked "waste" which makes it the deck pumpout fitting for a holding tank that may or may not exist on your boat.. If there's a hose or pipe connected to it, trace it to see where the other end is. Also try to trace that pipe that appears to come off the toilet to find the other end of it.
I DO know what I'd do with all of it though: get rid of the toilet and piping connected to it and replace it with a self-contained system-- an "MSD" portapotty. The "MSD" designation in the model name/number means it has fittings for a pumpout line and vent line, and is designed to be permanently installed (actually just sturdier brackets than portables, so you could still take it off the boat if you absolutely have to), which means that although it's still called a PORTApotty, you don't have to carry anything off the boat to empty it.
A 5 gallon model is household height and holds 50-60 flushes...you'd need at least a 30 gal tank to hold that many from any marine toilet. No plumbing needed except a vent line and pumpout hose (you already have the deck pumpout fitting)--so no new holes in the boat...and -0- maintenance needed except for rinsing out the tank--which you can do with a bucket while it's being pumped out. Total cost including the pumpout hose and vent line is about $300--a fraction of what you'd spend for a marine toilet, holding tank and all the related plumbing needed. And the best part is, you have all the advantages of a toilet and holding tank without giving up a single square foot of storage space.
That's my $.02 worth for now...
--Peggie