Sewer Gas SolutionsTM is a highly-effective product for preventing dry traps due to water evaporation, but it obviously cannot solve every potential sewer gas issue. If sewer gas odors persist after using our product, sewer gas infiltration may be caused by one or more of the following:

  • Loose, cracked or otherwise damaged pipes (often caused by the drain lines being impacted by items stored under the sink) allowing our product and water to drip or leak out of the trap.
  • Cracks in vent stacks or waste lines (most common with cast iron).
  • Hydronic syphoning (usually from undersized pipes or restricted vent stacks).
  • Failing wax ring (usually from a loose toilet or failure to replace the wax ring following a floor system modification).
  • Failing neoprene ring on saddle mounted toilets (usually from a loose toilet).
  • HVAC condensate lines plumbed into the water lines post trap.
  • The absence of an installed plumbing trap (common with DIY installations).
  • Entrainment and distribution via HVAC system (usually from a vent stack too close to an outdoor air intake or a high parapet wall).
  • An actual natural gas leak (since natural gas has no odor, odorants are added to help in detecting its presence before concentration reach dangerous levels. The odorant is usually methyl mercaptan, which has a sulfur odor and can be detected by smell at around 2.0 parts per billion.
  • A waste vent line that does not penetrate the roof, but is in the attic or plenum space instead (usually the result of forgetting to reinstall the vent line through the new roof during a reroofing project).
  • A hardened or stuck rubber gasket in an air emittance valve (AEV), which are common one-way flow caps with a limited life span (typically, the rubber valve becomes stuck in the open or closed position.)
  • A dead and decaying animal (usually a rodent or large lizard) in a wall cavity or behind a cabinet (but on occasion, a deceased would-be burglar who got stuck in the HVAC).

If odors consistent with sewer gas are present, you should consider consulting an indoor air quality professional.  For a qualified IAQ specialist near you, visit the Indoor Air Quality Association (IAQA) at and use their “Find A Pro” feature.

For more information on sewer gas prevention, check out the Indoor Air Quality Association (IAQA) Tech Tip videos at:


What Should I do if I think I smell sewer gas?

  • Try to determine whether or not you are actually smelling a natural gas leak.  If you suspect that what you are smelling is natural gas, immediately leave the building, go outside and report the odor to your gas utility company.  Do not use your cell phone inside the building or do anything else that might cause a spark, as natural gas is highly flammable.
  • To prevent sewer gases from getting into your building through your plumbing system, make sure that every drain in your building has a U or P-trap attached underneath. Every sink, shower, bathtub, toilet, washing machine drainage pipe, basement floor drain, etc. should have a trap to prevent gas from the sewer main from getting inside the building.  Sometimes basement floor drains inadvertently get covered with carpeting during a remodel, so you may have to do some exploring if that may be the case.  The most common cause of sewer odor is when the water evaporates out of an unused or seldom used drain; to prevent this, pour water down the drain followed by Sewer Gas SolutionsTM, per usage instructions.  With Sewer Gas SolutionsTM, you only need to check and refill the drain every three to six months. Without Sewer Gas SolutionsTM, drains should be checked and refilled with water every one to two weeks.
  • Sewer vent pipes exist to help sewer mains vent through the pipe into the outside atmosphere (rather than inside a building). Clogged, congested (or non-existent) vent pipes can create a build-up of sewer gas, potentially creating enough pressure to allow sewer gas to push through the water in a p-trap. Ensuring that you have adequate and fully functional vent pipes for your building is essential to the proper operation of your plumbing system. If in doubt, consult a Indoor Air Quality Specialist.

Understanding the Hazards and Potential Sources of Sewer Gas:

  • Concentrations of specific sewer gas components vary dramatically depending on time of day, what is upstream, ambient temperatures, nearby line jetting, building pressure (i.e., a negatively pressurized room will draw in more sewer gas than a positively pressurized room).
  • Sewer gas can contain noxious chemicals and substances at concentrations that can create adverse health effects such as: nausea, irritation of mucosal membranes (eyes, nose, throat, lungs, etc.), headache, etc. Symptoms of sewer gas exposure are often nonspecific to any single contaminant.
  • The presence of sewer gas is sometimes difficult to identify and pinpoint using your senses because:
    • Sewer gas odors are different depending on the time of year, the time of day, the sewer system usage (residential, commercial, restaurant).
    • People have varied levels of olfactory sensitivity (ability to smell).
    • People have very different descriptive abilities – what one person describes as a “musty” odor may be described by someone else as smelling “acrid” or like a “locker room.”
  • Often mercaptan from a sewer is mistaken for mercaptan added to the otherwise odorless natural gas. This causes mistaken reports of natural gas supply line leaks.
  • Sewer gas can be accompanied by pest (insect, arachnid, rodent) infiltration from the main sewer line, exacerberating the hazards.
  • Sewer gas can enter a structure from a variety of sources:
    • Floor drains (especially when hidden from view, neglected or infrequently inspected, or hard water-damaged)
    • Sink drains (often subject to plumbing leaks, located in infrequently used residential, vacation or commercial rooms)
    • Shower drains (particularly those infrequently used or used for storage)
    • Toilets (from infrequent use, loose toilet fixtures, wax or neoprene ring damage or failure)
    • Sewer clean-outs (such as from missing, loose or damaged pipe caps)

Tips for Plumbing Maintenance and Prevention of Sewer Gas:


  • Service manually filled floor drains regularly (QAQC)
  • Service trap primers regularly (QAQC)
  • Soften water to avoid hard water build-up and resulting damage
  • Run water in all unused fixtures regularly (QAQC)
  • Inspect saddle mounted and floor mounted toilets for movement regularly
  • Inspect wax and neoprene toilet rings periodically and replace the wax or neoprene ring any time a toilet is detached
  • Do not use wax rings where neoprene rings are called for and vice versa
  • Install drain plugs (rather than using towels or rags) during renovation or removal of water fountains, toilets, sinks, etc.
  • Install backflow prevention devices
  • Use Sewer Gas SolutionsTM in drains that are underused, unused, or unattended for long periods of time.