Bad odor when flushing black tank

I disagree about the tank not draining well with the roof vent(s) clogged. Mine drained fine with the roof vent clogged. There is enough air available along with the discharge flow, and also forced around the toilet seal.

My issues were actually with both the grey and black tanks blocked from wasp nests, but my major issues were with the grey tank. That vent pipe was installed about 2-3 inches low into the grey tank, (and 2-3 inches below the roof, which indicated the installation problem) and when the tank was nearly filled, the vent inlet was below the water level, and could not then vent. The foul vapors would then vent through (overpower) the under sink vent, or adjacent sinks. I plumbed a flexible line bypassing the under sink vent directly to the exterior, which solved the problem.

The bathroom sink, shower, and toilet are vented through the roof, the kitchen sink has AAV under the counter. When I dump, I close the grey tank valves and then dump the black.

When we bought our current rig two and a half years ago, I had that problem. DGS would not stay anywhere near the RV when I dumped and he has to use a bag in the wilderness. It was awful!

Suggestion on here was replace the AAV on the Grey Water system. I did that and no smell. I decided at that point, that I knew nothing about RV sanitary tanks. I dump, close valve, flush with the Tornado System, dump again and if not clean I flush and dump again.

A few weeks ago I forgot and we had both Fantastic Vents going. Thought I died and been sent to the feeder pens on I-5. Do one thing at a time the first thing is to be sure the vents are closed. Mine shut off automatically when closed.

Thanks for the info, I know that the vent works or it wouldn't drain quickly. I'll get a new toilet flange gasket. All of the repairs were done by the RV Doctor in Fort Meyers, worst place ever. I had to redo all of their repairs and they wouldn't fix them because their tech have twenty years in the business and know what they are doing.......I'm not going to go into details here, but suffice it to say I can believe they screwed that up to as I have had to redo everything except the new vinyl floor that they did, and I still have to replace the door frame they damaged when they installed it.

Might be an issue of tank not getting properly cleaned. If you have a couple of weeks of non-use then consider using septic tank cleaner and allowing it digest/clean everything in tank - read up on geo method as well. Might be decent alternative b4 tearing up the toilet etc.

tank would NOT drain very well IF VENT was blocked...that is NOT you issue

Toilet to tank line repaired sorta.then you finished up fixing it

Toilet had to be removed for that type of repairs
A NEW floor flange seal SHOULD have been installed when toilet was reset.
It is a foam seal...good when new/installed...not intended for reinstall

Get new floor flange seal and replace that crushed old reused one.

In your original post you said you closed the dump valve with the flush on. Quote "...then I close dump valve for a couple of minutes with the flush system on" if your vent is clogged or restricted that could be the cause.

I’d reseal between toilet and floor first as that’s the easiest.

Does the toilet down hold water?

Is your through the roof vent of the black water tank possibly blocked?

Doors closed, Fans Off. I open dump valve first, and then turn on flush. I'm thinking of checking the gasket on the bottom of the toilet. I recently had some repairs done by a very incompetent repair facility. They had to put in a new connecting pipe between the toilet and the black tank. What they did leaked and I repaired it myself, no leaks since, but I didn't check the toilet gasket.