First time with any of my RV's that I developed a strong methane gas smell emitting into my TT (nasty)...., originating from around the toilet. What's interesting was the tank was emptied & flushed throughly two months prior, and the smell didn't start until I arrived at my boondocking destination last week. So at the campsite I .......,
* Checked the rooftop stink pipe, all clear.
* Checked all P-traps/vacuum breaker valves.
* No visible cracks around plastic toilet.
* Toilet bowl seal fine.
* No dead mice/nests.
* Purchased and installed a new flange gasket.
* Added about 1/3 water and chemicals.
The above tasks didn't work, so the next day I filled the tank about 2/3 thirds full, dumped in a couple buckets of water/Dawn mixture, hitched the TT back up and headed to a State Park 12 miles away for a dump/flush. No sign of any tank leaks under the TT at the dump station. Headed back to my boondocking site....., the smell persisted from around the toilet, but not as bad.
* Added some tape around the floor base of the toilet and a the hand flush handle ......, smell still noticeable.
* R&R the toilet again, installed another new flange seal, re-taped..., same gas oder problem.
Before heading home a few days later, I did another tank fill and dump/flush, still had the methane gas emitting from around the toilet. I wasn't using the toilet while boondocking.
Long story short, dropped the TT off at my local RV repair facility yesterday. He will do a detailed inspection of the tank checking for cracks, all pipe/flange/stink pipe connections, remove and inspect the assembly seam of the plastic two-part Thetford toilet, etc..
I'm also having the tech confirm that the stink pipe isn't extended to far down into the tank. As an added venting aid, going to have installed a roof product called the "360 Siphon Vent", can't hurt.
The 360 Siphon link: 360 Products Inc
I'll report back the RV tech findings in a couple of days.