I have an odor under the bathroom sink. The sink is right next to the stall shower. I poured bleach and let it sit - nothing gets rid of the smell. We have a different type of sewer system here - the tank is under the ground and it gets pumped out into sewer lines. We tried regrouting the shower, it was leaking at one time. Is it possible for an odor to be coming from the tank under the ground through the drain. There is no other odor coming from the other drains in the same bathroom. Any advice would be appreciated

Lets start wiuth the basics, is the smell sewage or musty and moldy?

In addition to Ballengerb1: Any wetness under the sink, inside the cabinet ? Any wetness around the shower, on the walls ?