Catalina 30 TRBS #2889 "Northern Light"

If air circulation is the answer for limiting holding tank odor, the single stanchion hole isn't an adequate vent. While I don't doubt Peggy Hall's advice that encourages lots of air circulation, I suspect the only way to get truly adequate air circulation would be to design a system that more or less looks like a municipal sewage plant, open leech pits, aeriator fountains, and all. It would work really great but might not be socially acceptable on a boat, at least not one at a dock or in a mooring field.

Meanwhile, if I could do two things here's what I would do...

1. Vent the tank at the top of the mast. Then it doesn't matter how much it smells. Terminate the vent with some sort of venturi. Between rising hot air and the venturi effect, there would always be negative pressure on the holding tank. I haven't had time to do that yet.
2. Install a Home Depot housing ($18) and replacable charcoal cartridge ($7.) That's much less costly then West Marine's throw-away unit ($60 per year?) and less painful than suggestion #1, above. The charcoal filter, along with a thorough cleaning of the hose and compartment surfaces, takes care of the odor issue. Replacement of old hoses when odor permeates through is a periodic necessity.

This filter housing is mounted behind the port seatback cushion. The hose on the right side dips downward on it's way up to the base of the stantion vent which requires that hose to be vacuumed prior to winter to ensure there is no liquid in that line.