I' m pretty sure he means stanchion...
Which means the boat has to be a Catalina...Catalina is the only builder I know of that runs the holding tank vent into a rail stanchion. The only air source is a tiny little slit in the base of the stanchion, and it's easy to clog...because when the boat heels, waste in the tank spills out the vent.What I'd do to cure the problem: 1. Get the vent out of the stanchion...install a vent thru-hull.2. Move the vent fitting on the tank to the inboard side of the tank. This will prevent waste from spilling into the vent line when the boat is heeled.Meanwhile, about all you can do is keep the slit in the stanchion and the connection on the tank--both the fitting and that end of the vent hose--cleaned out with a screwdriver blade. You won't have to do it as often if you backflush the vent line (yes I know getting water into it through that little slit is a major challenge) every time you pump out and/or wash the boat.