I have a 99 450 caver. When I flush the toilet the smell comes from the holding tank vent. This boat doesn't have filters on the vents for the tanks. I'm thinking about installing some. Has anyone tried this.
Bought one at Defender, I think. Simple install, they come in two sizes. There is also a lot of stuff on the web about building your own. It's really just a piece of PVC pipe, end caps and fish tank charcoal.
Look up http://bigorangefilter.com . Mail order only to the states. Good alter to the Dometic filters.
Just built two out of ABS pipe, a union for opening and barb couplings. Two female 3/4 garden hose fittings fit into short lengths of hose and voila! I filled them with the "No Guff" charcoal recharge kit for 30 bucks. Next year, I'll have the time to run to the pet store for some activated carbon. Much cheaper than the Dometic cartridge.