Won't hurt anything, Henry...
But a couple of gallons of white vinegar should be enough to clean out the head discharge hose on 10 boats! If you just flushed it through, you put more in the tank than in the hose...and if your electric toilet doesn't let you flush it dry, what little did manage to remain in the hose was too diluted to do much good. If there's a low spot in the hose, that's the only place where any vinegar that did manage to remain in the hose had any opportunity to work. Here's what you need to do: Disconnect the hose from the tank and the toilet... put a plug in the lower end....pour undiluted vinegar down the other end...plug it or reconnect it...and wait 2 days. In 10' of hose, that shouldn't take more than about a pint. If the toilet isn't flushing freely after doing that twice, you have a different problem that vinegar isn't gonna solve. But C.P. might... 10' of hose between the head and the tank is the absolute MAXIMUM distance it should be--and that's only if the hose doesn't have any major bends in it. 6' is about as far as anyone will keep flushing long enough to move bowl contents...anything longer starts to leave waste in the hose. So you may have a genuine clog--a buildup of waste in any sag between the toilet and the tank. So you might just try putting some undiluted C.P down the hose (remove the hose from the toilet and just pour it in) and waiting a day, before trying vinegar again. However, replacing the hose may not be as impossible as you think: join the old and new hoses together by cementing (don't use clamps--you want a smooth surface...don't use duct tape--it won't hold) the ends onto a male-male coupler...pull the new hose through as you pull the old hose out. Even that may LOOK impossible, but better figure out how to do it, 'cuz sooner or later, you're gonna have no choice but replace that hose... 'cuz sooner or later it IS gonna permeate and start to stink.
