Regardless of any accumulated deposits or a Poop Pyramid, you should NEVER get an odor stopped or in transit.
1. Use Pine sol. Fill and flush the tank 3 or more times. Then leave empty, no chemicals. Put about a pint of pine sol in the tank thru the toilet. Kame sure the toilet bowl DOES hold that little water(1 cup or so). Drive the RV. See if you get Pine sol smell. IF NOT, then your Gray tank is the cause of your odor. IF it does smell of Pine sol, then you need to pull the toilet and check its mount on the down pipe to the black tank. Verify the toilet flange seal is GOOD(I doubt it after all these years). Regardless, you now replace the flange seal. Get this flushing tool and use it to help clean out that ridge in your tank.
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