Sewer Smell in Top Floor Sink

I live in a pretty new house, but I'm definitely getting a sewer smell whenever I run water in the top floor master bath sink. (It's only the sink on my side, not my wife's.) It may have started after I installed a basement bathroom, which I tied into a vent stack--a stub coming from the basement ceiling. Could this have been a cause? Could they be connected? What can I do about it?

Thanks.

sink

Pour a liquid drain cleaner down the sink's overflow opening. That should kill the odor causing material.

Success!

That totally worked! I just used a Clorox solution and no more smell. Thank you so much.