I have an intermittent sewer smell in my first floor bathroom coming from the toilet area. I have a double vanity, toilet, and shower in the 1st floor bathroom; and a single vanity, toilet, and shower in the 2nd floor bathroom. Both bathrooms have forced venting, if desired. All the traps are full of water. I checked both vent stacks on the roof and they are clog free. Several months ago the 1st floor toilet would gurgle when running the washing machine, but that does not occur anymore. There is no smell in any of the sinks, showers, or in the laundry area. I am on a septic tank system.
I have tile in both bathrooms, so double wax rings are installed. The water drains easily in all sinks/showers/toilets/washer. Do I need to reset the toilet? Should I installed an extended flange and use a standard wax ring? Should I extend the toilet sewer pipe to basically floor level so I only have to use one wax ring? What else could be causing the problem?