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 to provide good air circulation through the holding tank, I suspect the only way to get truly adequate air circulation would be to design a system that resembles a municipal sewage plant. Just think, a boat with open leech pits and aeriator fountains! On second thought it might not be socially acceptable, at least not at a dock or in a mooring field. Besides, heeling would present problems.

Back to reality...if I could do two things here's what I would do...

1. Vent the holding tank at the top of the mast. Then it doesn't matter how much it smells. I'd install some sort of venturi apparatus at the top of the pipe. Both rising hot air and venturi effect would always create negative pressure in the holding tank and keep fresh air constantly moving through it.
2. Since I haven't had time to do the above modification, I tried something else and it seems to be successful. I installed a water filter housing (Home Depot $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 filters are available at hardware stores and make a huge difference in the odor issue. Don't forget to do a thorough cleaning of the waste hoses and inner compartment surfaces every few years. Replacement of old hoses when odor permeates through is a periodic necessity. I believe Peggy Hall suggests a way to identify hoses that need to be replaced.

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

The filter is mounted in a space that is difficult to work in. If the housing is stuck shut after being closed for a year it's difficult to loosen it by hand in the confined space. Make sure you keep the housing wrench that comes with the filter!