@billwnc
You could call the forum store and ask them to review “THE BUILD LIST FOR THE 18.5” and refer to it as the cockpit drain hose to see if that list shows which size hose.
Information on the 18.5 can be found under boat info/Hunter resources/18.5. The keel was referred to as the wing bulb keel. Former dealer who introduced that boat for Hunter and purchased the last one built.
Also you may have either a Kenyon Isomat or Z Spar mast but you should be able to find a mfg sticker either on the mast or boom. If z Spar, go to either forum store or US Spars. Feel free to send a private message