Sewer gas smell coming from tub. Odor especially strong after tub/shower is used. Has an old "drum" trap. Have tried Draino, foaming cleaner, bleach, snake. Inspected vent pipe in attic which looks intact. Plumber came, changed wax seal on toilet; said he'd never seen any clogging of vent pipes in his career. If it wasn't cracked, then he didn't think that was problem. He said he didn't think drum trap was leaking because no water coming out of ceiling. No smell from any other drain in house. Have scrubbed to try to remove any "biofilm"

Hi Macorder...

Always tough to help with these kind of questions.

Could be that the drain pipe is partially clogged and the drum trap is gurgling/siphoning, in a manner of speaking, allowing sewer gasses to escape into the bathroom after a tub/shower, but the only fix here would be to snake the drain and/or clean the drum trap itself... ;)

Hard, if not impossible to access/clean an old drum trap, so most of the time we just replace them with a new drum trap. When the drum trap is removed we snake the drain with a large cutter head and wash the drain with hot water at the same time for best result.

I can't offer much more on this as it sounds like you've done everything you can, short of replacing the drum trap as I mention here.

If you'd like to discuss this more, just let me know, OK?

Mark

Thanks much Mark. Is it better to replace with different type of trap or does that usually involve too much restructuring? Drum trap is currently underneath linoleum floor.

If you have a drum trap in place I would replace with a similar drum trap.