There is another potential solution to many of our toilet issues. Yesterday, my wife and I had the first opportunity to use the new and recently installed camping/portable toilet, which I installed after removing our previously installed, from new, electric TMC boat toilet about 12 years ago, after the original manual TMC that came with the boat, broke down .
The trouble I had to go to to install that, plus the now required holding tank, in a boat never designed for such, I will not bore you with - suffice to say it gave me the most grief any boat system...ever..! When recently the motors seized on both holding tank pump and toilet, and even when replaced something was still seriously blocked, I had had enough, because even if I got it all going, the dearth of pump-out facilities still means huge issues getting the tanks emptied.
So, I removed the lot, blanked off the hoses and closed the thru-hulls...forever..!
I purchased a good quality portable loo, which is therefore not plumbed, with no pipes to block, Y-valves to worry about, and has its own holding tank, which can be legally disposed of here in the normal sewage system, and it was so simple, easy to use, and virtually silent, I wondered why I did not think of it before. And yes, I have it well secured so it won't 'fly' about in a seaway, don't you worry about that..!
For the length of outings we go out for, (and I suspect many on the forum), the volume held with be plenty, and if further afield the treated contents can be dumped overboard in most areas anyway. Too good to be true..? Time will tell, but I suspect it is going to save me a heap of grief in the meantime, as when I think about it, any time we have had an issue bad enough to spoil any outing in the boat, it has been toilet related. Funny that...