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