We moved here 2 years ago in late August and when it got cold out, we would smell a sewer odor in the downstairs (basement, it's a split-level) bathroom/laundry room. We narrowed it down to a place where the smell seemed to be coming out of a small hole in the drywall where it met the floor. Never had a chance, though, to fix it, as just about the time we would want to do something it would go away.
It got cool recently, and it re-appeared, so we decided to investigate. We cut away the drywall on the other side of the wall, where the pipes were, expecting to find an exposed vent or something of the like. We didn't find anything, except that we did put some sealant around the vent pipe joints.
Then we focused on the bathroom. We decided maybe the toilet needed a new wax seal, so we took the toilet off to find ...... that the sewer pipe/toilet mount was never extended up over the 1.5" insulated floor of the basement, and to compensate, they just used 3 wax rings on top of each other.
Well, you can guess what happened...they deteriorated and water had slowly seeped out. Underneath the vinyl linoleum on the subfloor, soaked the subfloor, which was moldy, stained, and rotten.
We've since determined that was in fact the source of the smell, ripped out the damaged subfloor, and laid real tile down in its place. This was the toilet mount is flush with the floor, like it should be!
What do people think sometimes when they make repairs! Did they really think that would last??
The people who sold me my house did several "cover up/repairs/super cheap" IE not repairs, just to cover up issues temporarily just to sell the house. It doesn't surprise me. Said thing is the issue you had could have been easily and cheaply fixed.... before it did damage.
Fortunately it was the basement and contained to one area, so it wasn't too bad. We were going to redo the floor eventually, anyway, so better sooner than later I guess. We got a good deal on some clearance tile at Lowe's so I guess it was a good thing.