Sewage smell in bathroom sink

When I turn the water on in my second floor bathroom I get a sewage smell coming from the sink.I have 2 sinks in the bathroom both attached to the same drain each sink has a trap installed .All the sinks drain well and you do not get the smell anywhere else only in the seconfd floor bathroom.

Have you checked the trap?

You might try running something, like a coat hanger, down through the sink vent hole. Sometimes hair and other debris builds up in the vent area under the drain and emits an odor as it decays. Sometimes you can push it out with a coat hanger from the vent hole in the sink.

you need to add a vent pipe to the out side.lines are venting through the up stairs sink.just add a tee run pipe through the wall out side out side use a 90 degree elbo stand up with 5 foot section.this problem happen often on septic tank is in use.waste gases seek highest levels which is upstairs.you could add a vent pipe closest to main drain going out to the service would be better vent before going in the house.i put mine on the pipe going to my septic tank input right at the tank.and went up the wall past the roof line single story house vents above the roof so if you open upstairs window oder does no come in .

also put on a vent cap so leaves and debries and birds do not get inside pipe.if you have a outside vent pipe already bet you something is plugging pipe debrie field.

?both sinks or just one? Is either one new? Are you on a weell? Some newer sinks use plastic supplies that react ro some water. Search hanksan replys.

Both sinks they are new and only when the water runs it comes from the drain for sure .I have 2 traps installed one on each sink