Since you're asking about installation of a flush toilet, I assume your favorite sailing areas have pump out stations.
IMHO the easiest way to go is an MSD, with deck pump out, there are several to choose from. Does your boat already have a porta-pottie? Mine came OEM with a SaniPottie 965, 2.5gal. I upgraded to a SaniPottie 965 MSD, 5 gal, and plumbed it for deck pump-out. But it can also be manually dumped if necessary. And can easily be taken off the boat for a good cleaning.
There's a couple reasons I went with that one. 1) it fit perfectly into the same footprint of the old one's hold down brackets. I just replaced the old brackets with taller ones to accommodate a 5 gal holding tank. 2) I knew I wanted more holding capacity, and this 5 gal model added the least amount of height, considering the limited head room in the 26C's.
You could install a porcelain marine head with separate holding tank, I've seen pictures of 26C's with them installed. I didn't go with that because you then need to determine where the holding tank will go, and that would take up valuable space for other things, such as batteries, fresh water tank, storage, etc. That's why I think the MSD is the best way to go, it takes up no more real estate than the head you already have. And the installation is much easier.
The Sealand Deluxe "features a pressurized water tank for powerful, freshwater flushing action at the touch of a button". Which might be nice, I looked at it and noticed the lever you pull to dump had a plastic shaft, which I was sure would break someday. Sure wouldn't want to be stuck out sailing with no way to close the holding tank! The SaniPotties use the same kind of holding tank valve used on RV's with a SS shaft. They're made of high density polyethylene. I still have the OEM one, still looks and works like new, after 22 years! Plus all the parts are easily replaceable. Same design, same parts all these years later. When there's a good design why change it!
I bought mine from this place, they also have all parts available.
http://www.northeastsanitation.com/...in_page=product_info&cPath=19&products_id=237
I suppose a porcelain marine head is the closest you'll get to a residential type flush toilet, but may be somewhat impractical for our boats. MSD with deck pump-out is the next best thing in my view, they use water in the bowl, and there's no unpleasant smell when you use the right holding tank treatment.
Here's my installation.
No hose clamps yet in this picture, but you can see how easy it is to disconnect the hoses for manual dump, or removal for cleaning.
It's easy to run the hoses straight up for pump-out deck fitting and vent. The cabinet I made holds and hides the hoses nicely.
http://s33.photobucket.com/albums/d64/doug91mac26s/Head/
-Doug
