Originally Posted by tdw
What I fail to understand is having fresh water flush.
Me too. The smell generated by stale sea water is instantly perishable. I pump the loo through when we arrive on the boat, the smell is gone in moments and does not return at any time while we're still on the boat. It only returns if the boat is left unattended for three or four days.
When the loo doesn't flush because you have run out of fresh water, being able to switch it to sea water seems to me like a very hollow victory.