Are you certain that isn’t the thru fitting for the holding tank discharge? Just curious, because I had a 88 Hunter 33.5 that had a gate valve for the holding tank waste discharge; all of the remaining thru hull assemblies had bronze ball valves. I don’t have a clue as to why Hunter used gate valves for the holding tank, other than reduced costs. Sort of general knowledge that gate valves are not a good idea for marine thru hull applications. Seeing your gate valve setup leads me to believe that it is probably original to the boat; 39 years. Needless to say, it is past time to replace the entire assembly preferably with a bronze seacock or at least with bronze ball valves. I replaced all of my Hunter thru hull fittings, valves, & tailpieces with bronze & fabricated new backing plates as the plywood plates that Hunter used were rotting. Definitely ditch the pvc/hose fitting & use a bronze tailpiece with double clamps on the hose. Must have been a plumber who did that repair! Don’t know what other maintenance / repairs are planned; however, this requires immediate attention.