There is a very strong odour coming from the bathtub drain for the past 2 months. I have poured bleach, baking soda, etc. down the drain and it helps temporarily, but the smell always comes back. A plumber I had out didn't seem to have any answers. The house is about 45 years old and we have never had this problem before in the 17 years we have lived here.
Answer:
It appears you'll have to get to the drainage line under the tub and block it. This may mean disassembling the ceiling under it or the wall behind it or both. Once that's done, you can take off the cap that covers the overflow inlet. Plugging the tub drain and then filling this overflow line with bleach should do the trick for you. You might even try getting a long handled bottle brush in there to scrape off the soap build-up. Leave the bleach four or five hours before draining the line, using the bottle brush again and then re-assembling the drain.
