Headshot of a homeowner holding his nose, likely due to sewage smells coming from a drain

It’s your worst nightmare—your shower and laundry smell like a sewer, and you have guests coming to stay for the weekend.

You know they would understand, but it would be much better to fix the problem, for your sake as much as theirs.

But where do you start?

The first thing to do is to put on your detective’s hat and try to identify where the problem is coming from. If you can establish the source, you stand a much better chance of resolving the issue.

This article will cover common sources of sewage smells, explain why you can suffer from these unpleasant odors, and what you can do about them. So, read on to find out how to gid rid of these bad smells.

But first, a quick answer to the question of what to do if you have noxious odors coming from your drains.

What Should I Do If My Drain Smells Like Sewage?

What you should do about sewage smells depends on the cause, but before calling a plumber, you should remove any blockages and check the P-trap is holding water. 

What Causes Sewage Smells?

Sewage smells can be caused by blockages, an empty P-trap, venting issues, or a simple buildup of biofilm from showering. 

Any unwanted smells in your home are far from ideal, but sewage smells are particularly unpleasant. In addition, they are often associated with methane gas, which can affect your family’s health, so they should be fixed sooner rather than later.

What Is Sewer Gas?

Sewer gas is not a single type of gas but a complex mixture of toxic and non-toxic gases that form because of the interactions of the various components of sewage within your plumbing and the town sewer system.

Sewer gas is emitted during the decomposition of the things we all flush down the toilet and wash down the drain.

Dirt sediment at the base and drain of a sink

You’d be surprised at what people dispose of down a drain. One of my friends is a landlord and was called out by a tenant no so long ago who had tried and failed to flush a used diaper down the toilet.

Unsurprisingly, this caused a blockage in the waste pipe and necessitated a plumber to deal with the obstruction.

Other things that people send into the drainage system include washing products, gasoline (yes, really), solvents, bleaches, food waste, and dead pets.

These materials break down in the sewer, giving off the components of sewer gas, which include hydrogen sulfide, ammonia, methane, carbon dioxide, and nitrous oxides.

Is Sewer Gas Dangerous?

Sewer gas is usually confined to the sewer, away from people, where it can’t cause anyone harm.

Of course, sanitary workers are exposed to sewer gas during work. Still, they have access to the required personal protective equipment and have appropriate training to avoid the harmful effects of the toxic gas.

A sanitary worker standing next to an open manhole cover in the street leading to the sewer

Sometimes sewer gas finds its way into our homes, through floor drains in a laundry, poorly-sealed or damaged pipework, or some other route. When this happens, we get that awful sewage gas smell in our living areas.

Although it would be better if the gas didn’t enter our homes at all, it is actually a good thing that it has a distinctive sewage smell because it alerts us to its presence, helping to avoid prolonged exposure and the negative health impacts that could result.

Most of the time, provided you are in well-ventilated areas, you are unlikely to suffer from the acute effects of exposure to sewer gas. However, if you are exposed to low concentrations for long periods, you could suffer from headaches, dizziness, fatigue, and more subtle symptoms, like poor memory or loss of appetite.

Let’s look at some health problems associated with exposure to sewer gas.

Health Impacts of Sewer Gas

Some of the components of sewer gas are toxic, and exposure to them will cause harmful effects on one’s health. In the worst cases, it can even cause death.

The seriousness of the harm caused depends on the person. Risk factors include smoking, drinking, previous exposure to chemicals, and general health.

Let’s look at some of the most severe impacts of human exposure.

Asphyxiation

Sewer gas that accumulates in an enclosed space can displace oxygen, leading a person to suffocate from lack of oxygen. Symptoms of oxygen deficiency can include dizziness, headache, nausea, and unconsciousness.

If the oxygen concentration is low enough, unconsciousness and death can occur with little or no warning. For example, oxygen levels of less than 12% (far lower than the average concentration of 21% in the air) could cause a sudden onset of unconsciousness.

Hydrogen Sulfide Poisoning

At low levels, hydrogen sulfide can irritate the respiratory tract and the eyes.

This gas has a distinctive rotten eggs smell at low concentrations, which can alert people to its presence. However, at higher, harmful concentrations, people seem unable to smell it, which stops them from being able to detect it.

In addition to the irritation to mucus membranes of the eyes and respiratory tract, hydrogen sulfide can cause nervousness, headache, nausea, and drowsiness.

At very high concentrations, hydrogen sulfide can make people lose consciousness and die.

A sign indicating hydrogen sulfide may be present in the river nearby

Fire and Explosion

Along with hydrogen sulfide, methane is one of the components of sewer gas, and both are highly flammable, which can cause fire or explosion when mixed with air in the correct proportions.

What To Do If Your Shower Drain Smells Like Sewage

Sewer gas not only has an unpleasant smell, but it can be harmful to your health, as we hope we made clear above. What is not so obvious, however, is what you should do about it.

The correct course of action depends on the specific circumstances and where the sewage smell comes from.

Ventilate The Room

No matter the cause, you should clear as much of the sewer gas as possible by ventilating the room.

If you have a window in the room, open it. If there’s an exhaust fan in the room, as often is in a shower room or laundry, turn it on.

Removing the sewer gas from the air in the room not only makes it more pleasant to be in but also reduces the risk of you suffering from any adverse health effects from exposure to the gas.

Ventilation is a critical topic for the health of people living in your home, as well as for the fabric of the building itself. We’ve put together an article on the subject which you might find interesting.

Check The Shower Trap

Closeup on the inner mechanisms of a shower trap
Courtesy of Dallmer

The trap is essential to your plumbing and typically prevents odors from entering your home. But it can fail to provide this function under certain circumstances, so if your shower drain has a sewage smell, this is one of the first things you should check.

Does the Shower Trap Have Water in It?

The first thing to look at, mainly if the shower hasn’t been used in a while, is if the shower trap has water in it.

Normally, the trap holds a small amount of water which acts as a seal to isolate the air in the room from gases in the sewer. However, if the shower has been long out of use, the water that should sit in the trap might have evaporated, leaving a clear pathway for gas in the waste pipe to diffuse into the room.

Filling it up with water again, either by pouring water from a jug or bucket or by running the shower for 20 seconds or so, should get it back in working order. 

Often this simple fix is sufficient to prevent the smell and saves you the hassle and expense of calling out a plumber.

Is There an Accumulation of Biofilm?

Over time, biofilm can accumulate in your drains from everyday shower use. Shampoo, conditioner, shaving cream, soap, not to mention skin cells and hair, all go down the drain every time we shower.

These substances can build up along the plumbing walls, forming biofilm, and when this happens in the drain immediately downstream of the plug hole, they can cause sewage smells. Sometimes they can even block the drain partially or entirely, which impedes the flow of wastewater and makes the rancid smell worse.

There are several ways to go about fixing this problem, but they all come down to giving the drain a good old clean.

A gloved hand removing the cap of a shower drain with a buildup of hair and dirt attached, in preparation to clean it

Some people swear by a mixture of baking soda, white vinegar, and hot water. Pouring the hot water down the drain, closely followed by a cup of white vinegar, and finished with a cup of baking soda can work wonders.

There will be some fizzing, and you might see foam rising back up into the shower floor but leave the mixture to work for 10 minutes or so and then come back with a suitable brush or cloth and a healthy dose of elbow grease.

The vinegar and baking soda will have loosened the biofilm, making it easier to scrub off the walls of the pipework.

Some people recommend using a paint roller, which is the correct size and shape to get right in among the dirt and give the trap a good clean. We suggest using whatever works for you.

What To Do If Your Laundry Room Has a Sewage Smell

If the laundry room has a sewage smell when doing wash, it doesn’t take a genius to guess that the problem could be something to do with your washing machine. However, it’s not apparent to the untrained eye what the problem might be.

Usually, the problem is to do with the drain hose, which might have been incorrectly installed. Everything could look fine on the surface, but if the hose had been pushed too far into the drain, it could have gone beyond the water sitting in the P-trap.

Check the P-Trap

There is a P-trap on most drains in your home, and you will probably have seen them under your kitchen sink or behind your toilet.

They have a “U” shape, which contains water in the dip of the bend that seals off the sewer gas from the air in the house, preventing gases from moving along the drain and into your home.

A PVC P-trap laying on a tile floor

If the flexible washing machine hose is forced too far along the drain, it will pass through the P-trap, bypassing it altogether.

Unfortunately, this means there will be no water in the P-trap to create a seal, and those unwanted sewer gases will soon find their way along the drain and into your laundry room.

The fix for this is simple—pull the flexible hose from the drain to just above the P-trap (about eight inches into the drain).

This simple adjustment will ensure that the P-trap is not bypassed and will operate as usual, preventing the sewage smell and keeping your laundry room smelling like laundry.

Check Your Plumbing Vents

If you have a sewage smell in your shower, there is a possibility there is an issue with your plumbing vents. The vents allow air into your drains so the wastewater can flow easily from your home and into the sewer.

If your home had no vents, the wastewater would not be able to flow down the drains properly. Instead, it would gurgle, just like a bottle turned upside down.

If you were to drill a hole in the base of the bottle after you turned it upside down, air would be able to enter at the top, equalizing the pressure above and below the liquid inside and preventing the suction effect that causes the gurgling.

Hence, no gurgling, and the water would flow out smoothly. This process is analogous to the function performed by your plumbing vents.

The vents also allow the smells and gases present in the drains to escape to the outside atmosphere.

a plumbing vent sticking out from the roof of a home
Courtesy of Eyman Plumbing, Heating & Air

 If they are clogged, you will likely experience some problems, including:

  • Gurgling or glugging toilets and drains
  • Sluggish drains that take a long time for water to flow away
  • Foul smells

The fix for a clogged vent is to go out onto your roof and check the vent’s opening. However, this can be dangerous, so the best option is to call a professional who will be able to carry out the checks quickly and safely.

The blockage could be a nesting bird, a dead rodent, leaves, or other debris.

If it’s close to the opening, you can easily fish out the blockage to fix the issue. However, if it’s further down, you might need to open the walls to fix it, which is disruptive and expensive.

Another potential problem is that the vent is cracked or damaged, letting odors out into the house at the point where the damage occurred. Sometimes these odors can find their way into a shower enclosure, or other confined space, where they accumulate, causing unpleasant smells.

Summary

Sewage smells could be a sign that sewage gas is entering your home.

Sewage gas is toxic in high enough concentrations, and prolonged exposure at lower levels can cause health problems. Acute exposure to this noxious gas can be fatal in some circumstances, but such conditions are unlikely to arise in the home.

If your shower has a sewage smell, you should check the trap to ensure it is full of water and provides a seal to prevent gas from entering your home from the sewer. If there is no water, fill it up, which could fix the odor problem.

Alternatively, biofilm accumulation could be the issue, and a thorough clean could sort that out.

If your house has a sewage smell when you’re doing laundry, chances are your washing machine is incorrectly installed. Sometimes the flexible drain hose is pushed too far into the wastewater drain and bypasses the P-trap.

Pulling the hose out far enough for it to avoid bypassing the trap will fix this issue.

Finally, if you’ve noticed drains glugging when flushing a toilet or draining water from a sink, the issue could be a blocked plumbing vent. Unblock it, and those nasty smells could disappear.

If you need help on other plumbing-related issues, you might find our article about keeping your water bill down interesting. You can read it here.

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