Jimmy Sayavong wrote:

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


Each and every drain in the house has a "trap"
containing a small amount of water. That water sits
in the trap and prevents sewer gas from escaping into
the room.

Good article he
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





"Don Phillipson" wrote in message
...

"Jimmy Sayavong" wrote in message
et...

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 ,

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
(Ottawa, Canada)