How to find the source of a sewer gas smell in your house?

Even the finest craftsmanship in home construction can sometimes result in buried mistakes. One category of construction defect that could go undetected before the drywall goes up, and for years after involve some indoors opening to the sewer venting system. This could be the result of nails accidentally perforating a vent pipe or as reported by a couple of plumbers improper traps underneath tubs*. One source of sewer smell that we lived with for years was finally identified.

How? A plumber capped off all of the the vent pipes on the roof removing any of the normal (desired) exhaust of sewer gas. In the alley he opened the sewer access cap and sealed the pathway to the city, then attached the exhaust of a shop vacuum to the sewer access opening. This formed a closed system with no escape for sewer gas within the home, unless there was an unexpected venting of the system. After tossing a small smoke bomb into the vac and turning on  the vac blower he learned that the smoke was pouring out from under a toilet!

The toilet was lifted and properly sealed airtight to its drain plumbing. No more sewer gas smell.

  * Underused sinks and tubs can have their traps go dry and allow gas to vent into the house. These need to have some water restored to the drains monthly.

gs  11/23