[Carl n Susan]

Do you experience the smell at both the bathroom and kitchen sinks? If the small is only noticeable in the bathroom, and you are plumbed for a washer/dryer, then it is much more likely you have "stale" water in the lines. Sanitizing the water system does not resolve this. You have to flush the washer lines by opening them and running water through them.

Do a "Search" for something like "bathroom sink smell" to find previous discussions on this issue. Here is just one posting on the subject. Clicky