4blade1
Veteran Member
Welcome! I don't know if that age of boat had a holding tank vent filter but one could be added with a few hoses and a $150 vent filter. When you flush the water from the head displaces the air in the holding tank which has to go somewhere! If it is vented external which is usually the case then the odor can still make it's way back into the boat, (not ideal). The vent filter absorbs the odor and helping but not fully eliminating. They need to be replaced annually. Also the vent hose which is seldom checked could have crack's or have become disconnected from the tank altogether which would cause venting into the bilge. As an owner you sometimes have to be a forensic investigator.