Well Drat, Bob types and talks and thinks and posts faster than me yet again.
If you have a pedal-flush toilet directly over a 9-gallon gravity holding tank it’s most likely a Dometic (bought out Sealand) 711 or 911 Traveller. Pull the pedal upward to add extra water to the bowl.
If you have the common Y valve option, you can select pump-out from the side deck (the dock machine does the pumping) or your macerator motor for pumping over the side when over three miles out, and not in a No Discharge Zone such as the Keys. Never use a formaldehyde containing product because next time you empty at sea it would kill untold billions of “good” sea microbes. For an RV at a campground dump station that’s no problem. Also, many additives use ‘good’ aerobic bacteria that are killed off by even trace amounts of formaldehyde.
We’ve found the most effective odor control solution is to get a pump-out at a marina every 7 days while cruising. Some are free with gas purchase, or $5 and give the dock kid $10 to do it for you. $25 + tip at Montebello Quebec is our record to date. Buy and use your own deck pump-out adapter. The adapters the marina has may be old and worn and mis- threaded enough to cause an unwanted geyser. Make sure your vent line to the holding tank is not kinked or clogged with insect nests. We’ve tried all the additives and currently like Happy Camper with Raritan Kills Odors (also goes down the sink to drain directly overboard) and Raritan Cleans Potties (both cheaper online than at West Marine). Raritan says their products can not be used with ANYTHING else, but seems to work fine. You can often get the West Exterminator blue or Pure Oceans green stuff on Buy One Get One Free sales if you want to try them too. Good mixing in choppy waters can help.
Water in the bowl is the odor blocker. If your bowl won’t hold water for a week, the seals need to be replaced. Call Environmental Marine, seals come with replacement instructions; a 2-beer job. Mine only last 1-3 years but we cruise all year.
https://www.environmentalmarine.com/2-p ... es-310677/
After 10 years at the job, the sewage hose from the holding tank to the macerator (or deck pump-out if no macerator option) becomes permeable and could be replaced with the best quality sewage hose you can find if nothing else helps.
If you have the infamous Jabsco series 18590 pump, ensure that none of the 4 body bolts is broken internally by turning the nuts. The first earliest symptom of possible impending failure is that it blows apart and sprays sewage all over the under counter compartment when you turn it on. The ‘gasket’ is paper, the rebuild kit is $58 and the newer SS bolts last longer than the old bronze ones in the ‘tough’ environment they work in. Your fishbox macerator pumps may be the same.
https://www.amazon.com/Jabsco-18590-209 ... ag=mh0b-20
Many Brats have converted to the AirHead composting option for #2 (pee is diverted to a separate container you must cart to the restroom. Sounds like Fun). They are an irrepressibly enthusiastic bunch (although not only on the universally fascinating subject of sewage management.) Maybe I will join them someday.
Hope this is helpful.
Cheers!
John