Sooo... we're replacing the old valves and thru-hulls on our '73 Northstar 80/20 and for the life of us we can't figure out what one of them is for. There are two 1 1/4" and two 3/4"... one 1 1/4" is designated to the sink out, one was probably for dumping but due to Canadian laws was capped off... one 3/4" is intake for the
head. What might the other 3/4" be for?