I'll tell you what got me going on this. I design boats like these

http://home.maine.rr.com/rlma/Challenger_Class.HTM

and work with a very experienced shipyard that takes care of the
systems design. The boats are fast so weight is an issue. I started
by assuming the heads would be salt water flush. They said, "No, no,
it's got to be fresh water because of the smell. It's worth the
weight penalty of carrying more fresh water."

The boats do smell better than the salt water flush boats. Fresh
water flush obviously isn't practical on a 32 foot sailboat but this
might be the next best thing.

--

Roger Long