How to find and fix septic tank or sewer odors:

This septic odor track-down article describes how to track down the source of septic or sewer gases as a step in the procedure to diagnose, find, and cure odors in buildings including septic or sewage or sewer gas smells or "gas odors" in buildings with a focus on homes with a private onsite septic tank but including tips for owners whose home is connected to a sewer system as well.

Guide to Tracking Sewer Odors to Their Source

What makes the smell in sewer gas? Sewer gases are more than an obnoxious odor.

Watch out: Because sewer gas contains methane gas (CH₄) there is a risk of an explosion hazard or even fatal asphyxiation. Sewer gases also probably contain hydrogen sulfide gas (H₂S) In addition some writers opine that there are possible health hazards from sewer gas exposure, such as a bacterial infection of the sinuses (which can occur due to any sinus irritation).

Depending on the sewer gas source and other factors such as humidity and building and weather conditions, mold spores may also be present in sewer gases.

Track the septic odor strength to a source: The photo shows how this pays off. A family room over this crawl space had the strongest septic odors. An abandoned waste line was no longer connected to a bathroom but it had been left open in the crawl space, permitting gases from the septic system to enter that area.

Is the sewage odor stronger outside or indoors? If indoors, is the odor only at a specific bathroom or fixture? Perhaps there is simply a particular bathroom which is missing a plumbing vent.

If the sewage odor is strongest outside that suggests a septic or sewer gas problem in the septic or sewer system, but don't rule out unusual site or wind conditions discussed below. Track the septic or sewer odor source to its strongest point. Before tearing up your own property or drains or building, let's be sure the odor is coming from your property and not from a neighbor or other facility.

Before proceeding to the more detailed septic odor diagnostic articles listed at the top of this article, see if you or other friends and family members can make these simple diagnostic observations. Each of these answers can point to some of the specific odor causes we list in our detailed articles below. Don't worry if you don't know the answer, just collect what data you can and then proceed to the detailed articles we list below.

1. Where is the sewer or septic smell strongest? Indoors, or outdoors?
   1. Indoors odor tracking: on what floor of the building and in what room(s) is the odor strongest? This may lead to a specific drain, trap, plumbing fixture, or similar problem
   2. Outdoors odor tracking: on what side of the building is the odor strongest? Does the odor get stronger if you walk away from the building or towards it? Is the odor coming from your property, a storm drain, a neighbor's property?
2. How does the septic or sewer gas odor strength vary? Is the variation associated with:
   1. Weather conditions: sun, sun shining on certain sides of the building or property; rain, freezing weather, snow cover, wind direction.
   2. Time of day: odors may be associated with periods of plumbing system usage; also temperature and wind conditions vary by time of day.
   3. Season of the year: snow cover and freezing weather can make odors appear or disappear.
3. What plumbing or flooding or other events have happened that may relate to odors: such as septic flooding during area flooding, a burst sewer pipe, a sewage leak in a crawl space that was not cleaned up, a change, addition, modification, or repair of the septic system, sewer line piping, or other mechanical systems in the home.
4. Does the building water supply smell funny? Hot water and cold water both or just hot water?
5. When did someone first notice the septic odor or sewer gas odor? and How old is the building?
   1. Has the odor always been present or has it developed recently.
   2. What else happened? If the sewer gas or septic odor began recently, what changes in the building or events at the property can be placed at about the same time as when odors were first noticed? Have there activities such as remodeling, demolition, or plumbing repairs that may have disturbed or affected the building drain waste vent piping, chimneys, gas appliances, or use of chemicals? Dead animals?

Your answers to these questions will help you make sense out of the diagnostic suggestions in the septic or sewage odor diagnosis & repair articles that are listed below at CONTINUE READING .

Also see SEWER ODOR TRACKING for more site and weather factors in locating the source of a sewer gas smell.

And see WET OR COLD WEATHER SEWER ODOR GUIDE for additional odor tracing and cure advice for odors occurring during wet or cold weather.

Contact Us if you have other diagnostic suggestions or if you simply cannot figure out the source of a problem odor at a building.

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2020-09-14 - by (mod) -

I'm not sure how your smoke test was conducted but if it was a smoke test of the green waste and venting system and if that produced smoke in the building interior then clearly there's an opening in the system that needs to be found and corrected. Perhaps you can find a plumber who will pursue that question using a sewer line camera or if necessary some invasive inspection to trace your drain and vent lines where they are not already immediately visible and accessible

On 2020-09-13 by Alyce

Hello.

We have a rotten egg/sewer smell that occurs after we use our master bath shower. The smell is not in the master bathroom but starts in the hall outside of the master bath and affects the entire house. I believe the smell is transported by the HVAC system. We’ve had two smoke tests. No smoke from the first test but the second test produced diffuse smoke in the formal dining room, kitchen, and great room.

Unable to pinpoint where the smoke is coming from. We’ve worked with three plumbers - they can’t identify the source or problem either and frankly don’t interested in taking extra time to solve the problem. We have two AC blower units - we sealed the blower Unit doors and the smell seemed to get worse?? As I mentioned, the smell usually occurs after we use the master bath shower but can happen spontaneously as well. We/plumbers, etc., have evaluated vents on the roof, checked p- traps.

No problems identified. We’re thinking we may have the perfect storm - a crack/leak in the plumbing system that then transports the gas via the HVAC system. Any ideas?

Thank you very much.

On 2020-07-28 by Anonymous

@MB123, So were able to isolate the problem. One of the toilet seat in th house had a broken wax seal which was letting out the sweage smell. The AC units were picking the oder and spreading it in the entire house. Puzzel finally solved.

On 2020-07-25 by the_11th_hour

Strange "sewer gas" (does not smell like sewage but chemical-y) smell in master bath shower. Started a few days ago.

First day, started at 7pm and also was in the main bathroom bathtub, but fainter there. Stronger smell in the very back of the house right where the sewer pipe would go out from under the house and into the backyard. In other words, the shower with stronger smell is at the end of the line.

Opened the clean out in the backyard and water was flowing freely and swiftly. NO drains are clogged, nor slow, nor gurgling. Left a fan in the window to vent the smell the first night and smell was gone by morning.

No smell whatsoever for 3 days. Have use both showers, both toilets, kitchen sink, washing machine and dishwasher during those 3 days with no problem. (Home was built in 1978, renovated both baths in the last 5 years, but have done nothing new since then.) After 3 days, smell decided to come again, about 7pm, same as the first time. We cancelled the first plumber because the smell was gone that morning.

Have no idea how to proceed because we've never encountered anything like this. Cannot find my specific issue online and have been searching for 3 days now. Any idea of what we should do to diagnose, or how we should proceed would greatly appreciated!

On 2020-07-15 by MB123

We have had sewage smell issues in the housefrom last 3 summers now. The sewage smells only comes on hot ( mostly when temp is above 90) and humid days.

the smell is very sporadic and originates in any bathroom of the house, spreads in all the bathrooms and then the entire house. Finally desipates after 15-20 min. we have resealed all our toilets, No dry traps in the house.
We had our house remodeled 4 years back. And the problem started 3 summers ago.

Have consulted 3 plumbers already. All three gave different resolution. Smoke test is what one of the plumber suggested for any cracked vents. other said to put a whole house U trap in the main sewage line and the third one said to increase the length of exhaust vents on the roof.
Don't know who to go with.

On 2020-05-30 - by (mod) -

Kirsten

Sometimes the return air inlet for an A/C system will pick up odors and transport them through the building; do you think that can be happening in your case?

On 2020-05-30 by kirsten hastings

the sewer gas smell seems to come from the ac vent in the bathroom when the air conditioner comes on

On 2019-11-26 - by (mod) -

Joyce

Let's start with the diagnostics at

SEWER GAS ODORS in COLD / WET WEATHER

On 2019-11-26 by Joyce

We have a septic system for our home. Having trouble with a strong odor in my bathroom on cold days only. Kind of like a sewage smell. Have had 2 plumbers out and cannot find the problem.

On 2019-03-12 by Don

Greetings,

I live in a building where my apartment is inundated with a chemical "smell" whenever the wind is up.

At all other times it seems to hover outside the apartment door, It is not a rotten egg smell, but an unpleasant chemical odor. And moat times, not just windy days, the whole building, smells of it. The elevators, the party room, the common halls. To varying degrees.

I had the opportunity to ask 3 plumbers on a construction site to identify an identical smell in a basement we were all working in, and all three agreed it was sewer gas smell. My wife dismisses it is insignificant, and she does not always smell it when I do, but she smells it when it is strong.

My problem is figuring out what it is, before I call someone in. I need them to come in on a windy day, to insure they get a sample of what is going on. Or I need to do it myself.

Any ideas how I should follow this up ?

I thank you in advance for your assistance.

Don

On 2018-11-30 - by (mod) -

It sounds like you're being pretty thorough. Couple of other things I doing this process is a thorough cleaning of the bathroom and a check that the toilet mounting wax ring seal is intact or perhaps just gets replaced as part of that exploration since you have to pull the toilet to look anyway.

Let me know what your investigators tell you and I might be able to comment further.

On 2018-11-29 by Ted K

Thanks for these great articles. We’ve been working on a sewer odor issue in our house for the past few months. We found two issues inside of walls; one an abandoned vent pipe in the basement bathroom wall which I added a Studor vent on to fix; the other, a vent pipe in a first floor closet wall which had been cracked by a nail when the house was built.

Thought those fixes would solve the problem but we still have it in and around the basement bathroom and 2 adjoining closets. The problems began around two months ago in late September or early October. The problem comes and goes and doesn’t seem to correlate with changing weather conditions or variation in basement water usage. We have a shower, sink, toilet in the basement bathroom. There is a separate laundry room next to it with well-sealed ejector pit and pump. We get no smell in the laundry/ejector pit room.

The traps all have water in them and the fixtures and drains don’t seem to have the odor coming from them. We have been cutting a few holes in walls and ceilings in and near the bathroom with no success at finding anything other than the open vent next to the toilet, which I fixed but it didn’t resolve the full problem.

I have a plumber from Roto Rooter coming soon to do a smoke test and he’ll have a camera to inspect the vent piping internally. They say they can find the cause and resolve odor issues over 90% of the time. I hope they areright because we’re at our wits end with this. I’ve also got another plumber set up to do a peppermint test if the smoke test isn’t successful. It’s going to cost a lot for the tests and camera inspection but I can’t think of anything else to try at this point.

The only other thing I can add is that we had a new mound system with pump station installed 4 months ago. The existing septic tank was leak checked and it passed so it was not replaced. This happened a few months before the odor problems showed up. Do you have any advice or insights to help? Thanks for whatever help you can give us.

On 2018-01-08 - by (mod) -

Tim,

Might there be a bad check valve on the sewage pump outlet piping?

On 2018-01-08 by Tim

I have a sewage pump in the basement. Shortly after it runs, I get a strong sewage smell on the main floor of the house. All traps everywhere in the house have water in them. Much stronger in the winter, but that coincides with less use in the winter as my basement tenant only lives there in the summer. Any suggestions?

On 2016-01-11 - by (mod) -

Scott start by checking for a bad wax ring toilet seal

On 2016-01-1 by Scott4267@cox.net

We live in Phoenix where it doesn't get real cold in winter, but it does get cooler. We're on a septic system. In winter we have a terrible, nearly constant sewer odor in our master bath, only. We have four bathrooms, but the odor only comes into the Master. It seems to be strongest in the area of the toilet.

On 2016-01-09 by Tammy

I recently had my septic tank emptied and within a week the septic smell in my home was overwhelming. I have lived at this home for ten years and have never had foul odors.

Question: clothes waster makes sewer gas smells

(July 11, 2014) Roger M., Northern MI said:

Have sewer gas smell from septic tank when clothes washer is run!

Reply:

Look for

• A drain vent clog or missing vent that is causing siphonage of water out of nearby traps

Or

• clogged drainfield or septic line pipes that back up when exposed to the extra water volume of the clothes washer

...

Continue reading  at TRACK SEWER ODOR by WEATHER or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

ODORS GASES SMELLS, DIAGNOSIS & CURE - home

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