Not the toilet
Hi Bill. You bought a great boat. I have a '79, and IMHO it is the best small daysailer/minicruiser out there. There should be no toilet-related through hull on the boat. The only port-side through hull I have is for the sink in the head. Oday seems to have changed some minor details on the boats through the years, and the location of the through hulls may have been one. I have the one on the port side, forward of midships for the head sink, and one aft of midships on the starboard side that I believe drains the galley sink. I don't know for sure since I have never used the water "system" on my boat. The prior owner hadn't used it in the 12 years he owned the boat, and it needs total replacement, something I don't really have the time, energy or need to do.I doubt Oday ever made a toilet through hull as the boat was designed to use a porta-potti. I guess it is possible that one of the prior owners of your boat did retro-fit a marine head into the boat, but if they did, it is supposed to have a holding tank. Direct discharge of head waste is illegal within a certain number of miles off shore; I forget the exact distance, but I remember it was far enough for me to think I would never take an Oday 23 out that far. In any case, it would be a good idea to find where the through hulls on your boat lead to and make sure they're protected. You made a great choice of boat. Good luck.