Photograph of a home made septic tank in snowFixture Odor vs Sewer Drain Odor

  • FIXTURE vs SYSTEM DRAIN BLOCKAGE - CONTENTS: How to separate Plumbing Fixtures from Plumbing Drain System as the Source of Sewage or Septic Odors. Causes and cures for sewer gas odors diagnosed by making a distinction between fixture-related odors and main drain or septic system related odors. How to find and cure bad smells in buildings by narrowing down the investigation
  • POST a QUESTION or READ FAQs about diagnosing sewer gas smells: how to distinguish odors from drains from odors due to sewage backup or septic failures
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Sewer or Septic Odor troubleshooting:

Here we explain how to sort out the causes of a methane or sewer gas smell by distinguishing between odors at plumbing fixtures compared with odors due to drain. waste, or vent piping troubles.

How to Separate Plumbing Fixtures from Plumbing Drain System as the Source of Sewage or Septic Odors. The photograph at page top provides a lot of septic odor diagnostic information, as we will elaborate here.

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Diagnosing fixture versus plumbing system blockage problems for correcting septic or sewer gas odors

How to tell a local problem at one fixture from a system wide plumbing problem:

Toilet wax ring Toilet installation

The photos just above show a toilet wax ring being replaced. Even if the toilet is not rocking on the floor - that is, it appears securely bolted down, if the wax ring is damaged sewer gases may leak out in that bathroom around that individual fixture.


Leaky cast iron building drain proven by septic dye (C) D Friedman

Odors caused by slow drains or septic drainfields: Included here but not common is the odor causing effects of a slow drain or drainfield: sometimes there will be a partial clog, causing septic effluent to back up and then recede as the drain empties.

In this case there may be no visible actual sewage backup into the building. The same thing could occur if the backup was caused by a failing drain field - the system may back up when there is a large volume of wastewater but then slowly recede. Or it might just create enough back pressure to push gas through the traps but no actual effluent.


How to diagnose partial drain blockages: If a partial drain blockage is the problem (watch out it could be due to a damaged pipe or tree roots in which case simply snaking the line is just a band-aid short-term fix), you might notice the problem more when the volume of wastewater surges, such as when doing laundry or emptying a bathtub.


An increase in the number of occupants in the building (and thus using the bathrooms) will also cause a surge in wastewater volume and may disclose these conditions.

Indoor Septic Odors with Outdoor Causes

Septic odors in the house could indicate that effluent is backing up into the house past the traps which normally intercept the odors, or entering at a building window or door which has had a plumbing vent terminated too close by. Such odors may or may not mean the septic system is failing. A backed up septic system does not always equal a failing septic system

See and also SEPTIC / SEWER ODOR SOURCE TABLE for details.

Outdoor Septic System or Sewer Gas Odor Sources and Causes

Septic Blockages & Sewer Odors in Cold or Wet Weather

Photograph of a suspicious wet area in deep snow on a residential property near the reported septic drainfield.A very common source of drainfield failure as well as an occasional source of septic tank back-flooding and occasional push of sewer gases (or sewage) back into a building is the failure to protect the septic tank and drainfield from surface runoff and ground water. An intercept drain may be needed. If this is the case septic problems (odors or backups) will be associated with heavy rainfall or wet weather.


If you are smelling sewage odors outside in cold weather but not inside be sure to check these items:

Check for wet areas that may indicate septic system effluent leaking to the surface of your own or nearby properties.

The photograph shows that even in deep winter snow, melted wet areas may be observed if they are active.

See SEPTIC SYSTEM INSPECTION & TEST GUIDE for a list of diagnostic articles.

Septic, Sewer & Sulphur Odor Diagnosis & Cure Articles


Continue reading at ODORS, DRAIN & SEWER LINE SOURCES or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.


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FIXTURE vs SYSTEM DRAIN BLOCKAGE at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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