Sewer Smell in the Bathroom? Why and What to Do


A sewer smell in the bathroom can be unpleasant and concerning. Here’s a brief summary of why it might occur and what to do about it:

Causes of Sewer Smell in the Bathroom

  • Dried P-Traps: The most common cause is dried-out P-traps, which are U-shaped pipes designed to hold water to block sewer gas odors from entering your home. If a sink, shower, or floor drain isn’t used frequently, the water in the P-trap can evaporate, allowing sewer gases to escape.
  • Blocked Vent Pipes: Vent pipes on the roof help maintain proper pressure in the plumbing system and prevent sewer odors from entering your home. If these pipes become blocked or obstructed, it can lead to odors backing up into your bathroom.
  • Leaking or Damaged Pipes: Cracked or damaged plumbing pipes can allow sewer gases to escape and permeate your bathroom.
  • Clogs: Partial clogs in the plumbing system can cause water to drain slowly, allowing odors to rise through the drains.

What to Do About Sewer Smell

  • Check P-Traps: Run water in sinks, showers, and floor drains that are infrequently used to refill the P-traps and create a water seal.
  • Inspect Vent Pipes: Ensure that vent pipes on the roof are clear of debris or obstructions. If necessary, consult a professional for inspection and cleaning.
  • Address Leaks: If you suspect leaking or damaged pipes, contact a plumber to assess and repair the issue.
  • Clear Clogs: Address any clogs in your plumbing system by using a plunger or plumbing snake. For persistent clogs or issues beyond your expertise, consult a plumber.
  • Regular Maintenance: Perform routine plumbing maintenance to prevent future sewer odors. This includes regular drain cleaning and checking for leaks or damage.

Is It Dangerous?

According to Healthline, small amounts of sewer gases are not dangerous. This is typically what you would have in your bathroom in case of a problem with your plumbing.

At high levels however, sewer gas toxicity can be expected. This is because hydrogen sulfide (present in the sewer gases) is toxic to oxygen systems of them body.

Apart from hydrogen sulfide, the other gases present in sewer gases are methane, ammonia and carbon dioxide. All these will result in sewer gases toxicity in high levels.

You will experience the following signs depending on the exposure levels:

  • Dizziness
  • Nausea
  • Vomiting
  • Fatigue
  • Headache
  • Heart palpitations

While the sewer gases in your bathroom may not be dangerous, they are just not pleasant to have and hence the need to fix the problem as soon as possible.

How to Get Rid of Sewer Smell in the Bathroom

In this post, I will start with the most likely source of the sewer gas smell in the bathroom and end up with the rare ones.

1. Fix Dry P-trap


Every fixture in your house with a drain has a P-trap. This is the U-bend under your sink which is named as such since it looks like an inverted P.

You can also see it on the side of the toilet bowl but the drain traps in shower and tub drains are not visible but have to be there.

A P-trap has 2 main functions:

  • As it names implies, it traps potential drain clogs, preventing them from clogging the drain line farther away. It is always easy to unclog a P-trap than to remove a clog several feet away from the fixture.
  • Its shape allows it to be full of water at all times. This water acts as a barrier preventing sewer gases from coming up through the drain but to instead do so through the plumbing vent.

Now, if you have a certain fixture in your house that has not been used for a while, the water in the P-trap can evaporate leaving the P-trap empty. This is especially common in guest bathroom sinks.

A leaking P-trap can also drain the water from the P-trap. Check if there is a pool of water under your bathroom sink. Leaking tub/shower P-traps are a bit harder to investigate.

With an empty P-trap, sewer gases will flow out through the fixture drain without any restriction and hence the sewage smell in your bathroom.

One simple thing you can do to fix this problem is turn on the bathroom sink faucet, tub faucet, shower faucet and flush all the toilets. In simpler terms, you want to run water through every drain for a few seconds.

The water will replenish the evaporated water from the P-trap. This is something you should always do after coming back from a trip/vocation.

In case you have a leaking bathroom sink trap, you can try to tighten the connections or replace the trap. That is usually a simple DIY that most homeowners can comfortably do on their own.

Leaking shower or bathtub P-traps are harder to investigate but if the ceiling of the floor below is leaking then that is good sign. It could also be that the P-trap is non-existent or even poorly installed.

You will most likely need a professional plumber to fix problems associated with bathtub and shower P-traps.

2. Check if you have S-traps


Do you know why S-traps are illegal? Better still, do you know the difference between P-traps and S-traps?

A P-trap as I mentioned is named as such since it looks like an inverted P. With a P-trap, the drain line is connected to a horizontal drain line which as you will realize is very important.

An S-trap on the other hand looks like an S and most importantly is connected to a vertical drain line. That is where the problem usually is.

When water is draining out of a fixture with an S-trap, there is no room for air to flow to the S-trap. As a result, a vacuum is created in the drain line which siphons water out of the S-trap leaving it empty.

With an empty S-trap, sewer gases will effortlessly flow out through the sink drain. That is why S-traps are illegal although most old homes still have them.

Check underneath your bathroom sink if you have an S-trap instead of a P-trap. Another sign of an S-trap is a gurgling sound whenever the sink is draining.

An easy solution for this problem will be the installation of an air admittance valve. Air admittance valves work like vents by allowing air to enter the drain trap during draining, preventing the creation of a vacuum and eventual siphoning of water from the trap.

3. Unclog the Plumbing Vent

A plumbing vent is the vertical pipe that is connected to your house’s main drain line and runs through the roof of the house.

It has 2 main functions:

  • It allows sewer gases to exit the drainage system instead of doing so through the drains.
  • Introduces air into the drainage system so that fixtures can drain fast.

Leaves, bird nests, dead birds and rodents, tennis balls, snow etc. can all clog a plumbing vent, preventing it from performing the above 2 functions.

The following are the signs of a clogged plumbing vent:

  • Gurgling drains
  • Sewer smell in the bathroom
  • Slow draining fixtures
  • Poor flushing toilets
  • Toilet bubbling when flushed

So, how does a clogged vent stack result in sewer smell in the bathroom?

If you have a clogged plumbing vent and you say, flush the toilet, the column of water flowing down the drain line creates what is known as a negative air pressure or in simple terms a vacuum inside the drain line.

As you may already know, it is not easy for a vacuum to exits. It will try to suck in air from the surrounding.

The problem is that there is water in drain traps separating the vacuum and the surrounding. What then happens is that water in the P-traps is siphoned inside the drain line and that is why you are likely to hear a gurgling sound from the shower/bathtub or sink drain after flushing the toilet.

The gurgling sound is as a result of the water in the P-trap being siphoned. You may also notice the toilet gurgling after the tub is drained.

With empty P-traps and a clogged plumbing vent, sewer gases will flow out through the drains and fill your bathroom.

Unclogging a plumbing vent is however something you can do on your own.

  • Climb to the roof of the house armed with a garden hose and locate the plumbing vent.
  • Check if there is rubbish at the top which you can easily remove with your hand.
  • Next stick the garden hose inside the vent and use it to probe and clear any clog that you may encounter.
  • Have someone on the ground turn on water to the garden hose. The weight of the water may just be enough to clear the clog.
  • If the garden hose doesn’t seem to do it, upgrade to a plumbing snake.
  • Push the snake down the vent until you encounter resistance.
  • Start cranking the handle until you go past the restriction. Remember that you should turn the cable but not twist it. If it starts to twist pull it up a little and then start again.

4. Clean the Drains

You may not believe it but perhaps the reason there is a sewer smell in your bathroom is because the drains are dirty. How is that possible though?

When cleaning our bodies, the products we use like oils, soaps and shampoos can form a sticky film called a biofilm, which is usually pink or orange in color inside drain lines.

This film can cause the sewer smell in the bathroom especially when combined with dead skin cells and hairs inside the P-trap.

The good thing is that cleaning drain lines is usually easy and cheap. This is how to do it:

  • Start by removing the bathtub stopper or shower drain cover.
  • Pour about half a cup baking soda down the drain.
  • Slowly add a cup of vinegar. Vinegar reacts very first with the baking soda and hence the need to add it slowly.
  • Let the reaction continue for about 15 minutes.
  • As the baking soda and vinegar are breaking down the biofilm and other types of gunk, start boiling about a gallon of water (a gallon for each drain).
  • Dump the boiling water down the drain.

While the baking soda and vinegar are quite effective in breaking down the gunk, boiling water will melt and dissolve everything left in the drain line leaving it smelling fresh.

Do this regularly to prevent the smell from coming back.

5. Check the Toilet Wax Ring

A toilet wax ring is a round ring made from wax that creates a watertight and airtight seal between the bottom of the toilet and the drain line.

One main sign that the wax ring is no longer sealing properly is when there is a sewer smell in the bathroom and also when the toilet leaks from the base after flushing.

It is however important to remember that even when the wax ring is leaking, water may not pool around its base but leak through the floor.

The causes of a wax ring that will not seal are loose toilet mounting bolts, uneven floor, a broken closet flange among others.

If there is a problem with the wax ring, you need to replace it. Wax rings cannot be reused.

However, before deciding to replace the wax ring, check if the toilet mounting bolts are loose and tighten them. If that doesn’t fix it, replace the wax ring and shim the toilet if the floor is uneven.

This is how to replace the wax ring:

  • Turn off water to the toilet
  • Flush the toilet and hold down the handle to remove as much water as possible.
  • Remove the tank lid and soak up the water still left in the tank and the bottom of the bowl.
  • Disconnect the water supply hose from the tank.
  • Use a wrench to loosen the toilet mounting bolts.
  • Rock the toilet about to break the wax seal then lift it off.
  • Place it on its side on top of old newspapers or towel.
  • Scrape off old wax from the toilet and top of the flange.
  • Inspect if the flange is broken. If broken, have it replaced as well.
  • Place a new wax ring on the toilet and set the toilet. You may need someone to help you with alignment of the bolts.
  • Tighten the bolts and hook up the water supply line to the tank.
  • Flush the toilet a couple of times to make sure the new wax ring is not leaking.

6. Empty the Septic Tank

If you are on a septic system, you need to know when it is time to have it emptied. With a full septic tank, waste will start to backup through the drain lines starting off with the sewer gases.

If the tank is not emptied immediately, actual raw sewage will start to backup from not only bathroom drains but other drains like the kitchen sink.

Other telltale signs of a full septic tank are:

  • Slow drains
  • Sewer smell in the yard
  • Gurgling sounds from fixtures
  • Standing water over your septic tank
  • An overly healthy lawn

And basically that is how to get rid of sewer smell in your bathroom. I hope this guide was helpful.

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