It wasn't the Dometic 300 that caused the odor
Our new Hemi 282 RK started having the same odor symptoms that many on this forum have suffered through and I thought the same. The odor also permeated up through the bathroom sink cabinet and the bedroom wardrobe where the water hearter is stowed. So I called and Dometic graciously sent the new modified toilet, even though the service rep said my SN # was the modified one. They sent a new one anyway.
So the last night at the campground before I was going to install the new unit, I was sitting in a chair enjoying the great outdoors and just happened to glance under the belly of the trailer and noticed a drip drip drip from the underbelly. I thought my wife was watering her flowers or doing something until I realized she was on the same side of the trailer as me.
A little investigating caused me to crawl under the trailer and the drip was coming from where the waste pipe comes through the underbelly covering and I noticed there was about a 4 " bulge of the belly covering. The drip smelled of sewage. I got a bucket and my trusty Case pocket knife (don't leave home without one) and cut a 1/2 inch size hole in the covering and about 3 1/2 - 4 gallons of raw waste came flowing out!
OH OH! Cleaned and flushed the black tank, sprayed clean water up into the hole I cut to rinse out as much as possible and drove it to the dealer the next morning -- under warranty, let them put in the new toilet and sanitize the underbelly.
Well I explained what happened to my dealer and the service manager didn't think it was the toilet, but said they would take care of it.
What had happened is that the black tank which is secured by being set on 2 channels of angle iron for support had slipped off one of the channels and dropped down the 4 inches which depressed the underbelly covering. In addition the joint where the waste pipe exits the black tank had come loose (it's a slip joint) and while most of the black tank did exit through the pipe, the dripping inside had occurred since almost day one and finally accumulated enough to find it's way out.
The tank was reset, all connections replaced, and in addition the dealer (who by the way said they had never encountered this before) put an additional 2 stainless steel straps under the black tank to make sure it doesn't move again. They washed the entire undercarriage and used a commercial sanitizer to spray everything down before putting the covering back on the underbelly.
I never did replace the toilet and there is no more odor. A couple of ozone odor eliminators in the sink and wardrobe cabinets took care of the residual smell.
Mark, Vicki, & Scout THE dog
2015 Hemisphere 282RK
2010 F250 Super Duty
1992 Goldwing Aspencade