Time to raise some hatches and explore your boat.
Trace all your plumbing--and check all the hose clamps while you're at it too...find all your breakers and what's connected to each one...flip switches and find out what they turn on and off. 'Cuz if something starts smoking or you see water rising in the cabin, that's not the time START looking for seacocks, valves and breakers.Btw...antifreeze should only be flushed down the toilet as part of winterizing...and then it should ONLY be the non-toxic potable antifreeze, never automotive. As for how your toilet works, what make/model is it? However, all manual marine toilets work pretty much the same way: there's a lever on the top of the pump that switches the toilet from the "wet" or "flush" mode to the "dry" mode. Pumping the toilet in the "wet" mode simultaneously pulls in flush water and pushes bowl contents out...pumping in the "dry" mode empties the bowl and blocks incoming flush water. The toilet should always be left in the dry mode except when the toilet is in use.If the toilet doesn't bring in any flsuh water in the wet mode, make sure the intake thru-hull seacock is open (find it!). It--and all other seacocks--should always be closed when no one is aboard. If it's open, we need to find out what's wrong.You'll have to find your holding tank for yourself...'cuz your boat is old enough that the tank was added by a previous owners...which means it could be anywhere. That's an over-simplication, but enough to get you started. If I know the make of your toilet, I can give you a link to the mfr's site where you should be able to get detailed instructions. Meanwhile, you might want to check out the link below to learn how to maintain your toilet and tank.