Sewer gas smells could be caused by a break in your main sewer line. However, this is the worst-case scenario, and there are a number of other, less expensive problems that could be behind the smell. That’s why we usually won’t start with a smoke test—we’ll only use it after we rule out other causes or normal testing methods fail to find the source of a break. Possible reasons for sewer gas smell include: -Bad seals on toilets (likely if you only smell sewer gas in one bathroom) -Dried out P-traps on floor sinks or floor drains that no longer keep a trapped seal -Clogged drains -Blocked air vents In commercial situations, sewer pipes can easily be punctured by nails, even by hanging pictures. We often see issues in multi-tenant situations where one suite is doing renovations and accidentally damages a shared sewer pipe. Whatever the cause, our team has the expertise and tools to get to the bottom of it.