I have owned a 89 Hunter 30 for a year and it has always had "the head odor". Read and appreciated Peggy's work. Last weekend, we had a leak in the head and traced it to the vent line. found that when I pumped the head, the vent line connection leaked. So I had to cut the vent line (due to age) and rigged up the fresh water hose with a hose clamp to the vent line. My wife is watching on the dock. Finally the whole boat shuddered as whatever was plugging the vent line blew out. She didn't have a chance to see what it was. Now the odor is much better in the boat. AS Peggy might say "when all else fails clear the vent line".