Horrible smell from RV toilet - any recommendations?

My experience is that chemicals alone will not cure a stink. The only thing that I would add to Bobbo's post is that while you are checking the seal, also check the pipe between the toilet and the holding tank. It can break because of the stress and allow the smell to escape into the RV, as happened in my HR.

Bobbo wrote:
Chemicals are not the answer.

Well they may not be the answer you employ but they absolutely work.
They've been working for us for 30 years.
And your wrong about a toilet not stinking. If you don't treat the waste and you open the flush valve, it's going to stink.
If the valve doesn't seal perfectly, like most that are more than a couple of years old, it's going to stink.

Further more, treatments are cheap. Rather than jump through a bunch of hoops or worry about vents discharging in the wrong direction or any other mindless nuances of sewage storage, the OP can dump a 20 cent ounce of treatment down the toilet and be done with it.

Add lots of water. Dump at every opportunity. Use chemicals as Scott suggested. “Grease” the rubber toilet seal or replace it.

Chemicals are not the answer. If the seals are all good, no smell will be coming into the camper.

(These are in no particular order.)

1. Is there a little water sitting in the toilet at all times? If not, smells WILL enter. If it is not holding water, the seal needs to be cleaned or replaced.

2. Sometimes, the seal between the toilet and the floor fails. Mine did once. Remove 2 nuts, lift off the toilet, replace the seal, put the toilet back, replace the nuts.

3. The AAV (Air Admittance Valve) under the cabinet by the sink can fail, letting in odors. They run less than $10 at a big box hardware store. That is always the first thing I do, replace the AAV, because it is so cheap and easy.

4. Be sure the sink's trap is full of water. If it empties for some reason, it will let odors in. The same goes for the shower's trap.

5. If there is a vent in the bathroom that is open, sometimes, when the wind is JUST RIGHT, odors going out of the plumbing vent on the RV's roof can blow back into the RV.

I have had #2 and #3 happen to me, and have had #1 happen to some friends.

Use the chemicals that are designed for that purpose.