We have a sewer odor that suddenly started in our bathroom. At least I think it's a sewer smell (and not a dead animal). The odor seems to be coming from the toilet. The toilet bowl appears firm and secure, but the wax ring has not been replaced in many years. I know how to replace the ring but I understand that the problem might also be the vent. What test might I perform to discover if the vent is working properly and not blocked? Also, do you have any other thoughts on what the problem might be?