I seem to be getting a bad/sewer odor when flushing my downstairs, and upstairs toilets. The toilet in the master bath, does NOT have this problem. I thought my vent was possibly clogged....so I went to the roof and ran a house down, turned on water and it seemed to "help" the oder a little bit, but not totally. I have a septic tank, which was recently pumped out as well. Not long ago, year possibly, I replaced the downstairs toilet. I am thinking the wax ring didn't seal good enough?? But would this also cause the upstairs toilet to smell as well??