How long???
Till the next time the toilet is used. The idea is, you flush the vinegar ALL the way through to the holding tank before the boat will sit. It's only a cupful, so most of it will be kinda spattered against the hose walls. But that's enough to prevent mineral buildup. When you come aboard again and use the toilet again, the first flush will rinse it all out. If you live aboard, flush the vinegar (btw, WHITE vinegar only) through the system when the toilet won't be used again at least overnight.In another month, SOMEbody is bound to ask.....never mind. I'll just wait till they do.