Raw sewage smell in bathtub


I have noticed some foul "raw sewage smell" coming from my downstair bathtub (with standing shower) after the shower is turned on for about 30 sec or so.
I have tried the following tricks based on the info I got on the internet, but it does not seem to permanently fix the problem:
(1) Poor liquid bleech down the drain, let in sit over night and poor HOT water into the drain. This only worked for few days, and that foul smell came back. (2) Snaked thru the drain hole and passed the P-trap to push any hair or resedue built-up. I did that, and I did not notice any different at all !!
Any idea or suggestions are ver appreciated ,
Thanks in advance
JIMMY
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Domestic sewage systems also have a "stack vent" to let sewage gases out into the air at roof level. Yours may be blocked.
--
Don Phillipson
Carlsbad Springs
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Logically, if the vent is blocked, the foul smell should show up on ALL drain, right? why it is only the subject bathtub? I am really running out of idea here.
Thanks

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Jimmy Sayavong wrote:

containing a small amount of water. That water sits in the trap and prevents sewer gas from escaping into the room.
Good article here: http://www.plumbing-basics.com /
A blocked vent *can* cause the trap to lose its water. Usually you would hear some gurgling in the tub when a toilet is flushed, as one example.
Try this very, very simple test before you go on the roof to check the vents or things like that:
Next time you smell the odor- pour 1 liter of water slowly into the tub drain.
Does the odor stop? If so, then the trap was dry and the cause needs to be investigated.
Odor did not change? Trap was *not* dry.
Sometimes odors like this can occur due to mold growth in the parts of the drain which are *before* the trap. In a tub, this could be the overflow pipe or the short section of drain from the tub outlet.
Play detective for a while before deciding what to do.
Jim

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