About a year ago, my upstairs neighbor's toilet overflowed and came pouring down my bathroom vent. It took about 1/2 hour to finally stop dripping. And it was not urine. The smell seemed to have gone away after about a month or so, but sometimes I would still smell it, especially when I ran the shower. In the past couple of months the bathroom is beginning to stink more like sewage. I don't know if it is because of what came through the vents, or is something going on in the shower drain. Everything seems to drain okay in our home.