My house is more than 100 years old. I’ve lived here for 35 years. Lately, my downstairs toilet won’t empty out. I had a company come and they ran a snake down the bowl. The toilet still wouldn’t empty.
Then they removed the bowl and ran an electric auger down the hole until they could see the end of the auger before it went to the line between the house and the road.
They replaced the bowl then had me run water in the tub, sink and hold the lever down on the toilet for some time to see if there would be any back up coming from the main line. There was none. Also, there is no sewer gas smell.