What Causes a Sewer Smell In The Bathroom. Mike Holmes Blog.
What Causes a Sewer Smell In The Bathroom. Mike Holmes Blog.

What Causes a Sewer Smell in the Bathroom?

By Mike Holmes

Mike’s Advice / Bathroom Renovation

Wednesday, November 1st, 2023 @ 12:45pm

Why Is There A Sewer Smell In The Bathroom and How to Get Rid Of It?

We all have bathrooms and unfortunately, we’ve all been in bathrooms that smell – but hopefully, it’s not in your home. A bathroom can be a sanctuary for some, a place to wash up and a place to relax. The last thing you want is a constant lingering nasty sewer smell in the bathroom. 

But why does this sometimes occur? And what can you do to make sure it doesn’t happen to your bathroom? Let’s find out!


What Causes A Bad Sewer Smell At Home?

A sewer smell is essentially the smell of sewer gas, which smells very unpleasant like human waste or rotten eggs. The first thing I would recommend checking is the toilet bowl and toilet seal to rule out whether the odours you are experiencing are coming from the toilet.

Certain components of your plumbing system serve to block off-gases from your home. The offensive sewage odours you’re smelling might be explained if these seals dry out or become loose. The seals around the water traps should be checked to ensure they’re not worn. These are found under every drain in your home —they are referred to as a P-trap or S-trap.



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Importance of Getting Rid of Sewer Smell in Bathroom

Follow my advice and do not let this sit. I know some homeowners might keep saying I will get to it another day. Another day is now and you don’t want to have to smell that unpleasant smell any longer than is necessary!

Rotten-egg smell is a symptom of both septic gas, which leaks in through the plumbing, and toxic drywall, which off-gasses hydrogen sulphide. If the house has been vacant for a while, dried-out traps might be letting in septic gas, which is lethal in large doses.


Common Causes of Sewer Smell in The Bathroom

Common causes of sewer smell in the bathroom can be from a dried-out P-trap, a blocked or damaged vent pipe or sewer pipe, a leaking toilet seal or a build-up of organic matter.


Mike Holmes inspecting plumbing.

Rotten-egg smell is a symptom of both septic gas, which leaks in through the plumbing, and toxic drywall, which off-gasses hydrogen sulphide. If the house has been vacant for a while, dried-out traps might be letting in septic gas, which is lethal in large doses.


Dried-out P-trap

That curved section of piping under your sink or shower is the P-trap. Its purpose is to keep sewage gases out of your bathroom.  When the P-trap dries out, it no longer seals out those smelly gases. 

Learn more below on how to fix this issue and keep your bathroom smelling fresh.


Blocked or Damages Vent Pipe

The vent pipe ensures that your plumbing system has enough airflow. This stops water from being sucked out of your traps and allows sewage gases to escape. If your vent pipe is blocked or damaged it could be the cause of the bad smells.


Broken or Damaged Sewer Pipe

Waste is transported from your home to the public sewer system by your main sewer line. You can encounter unpleasant odours and other problems when it’s damaged or broken.


Leaking Toilet Seal

Your toilet’s base is sealed to the floor and the sewage pipe by the toilet seal. This is sometimes referred to as the wax ring. A broken seal could allow gases to enter your bathroom, and cause a nasty smell.


Build-up of Organic Matter 

Over time your drains may become clogged with organic material like hair and soap scum. This can create a breeding ground for bad odours. You can prevent an organic build-up in your drains by avoiding the use of excessive amounts of toilet paper and flushing foreign materials down your toilet.


So now that you know some of the common causes, let’s discuss these further and how you can fix them to get rid of that bad sewer smell.


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How A Dried-out P-trap Can Cause Sewer Smell

The P-trap is the curved section of pipe located beneath your sink or shower drain. Its shape allows a small amount of water to be trapped, creating a seal that prevents sewer gases from entering your bathroom. 

Water enters the P-trap when it runs down your drain, filling it with water. Any gases from the sewer line below are blocked by the water barrier. 


How a dried-out P-trap can cause sewer smell

The water inside the P-trap might evaporate over time, allowing the seal to become dry and letting bad scents into your bathroom. This can often happen if a particular drain in your bathroom isn’t used frequently. Like if you have a guest bathroom or shower that is not used regularly.


Ways to fix a dried-out P-trap

If you suspect that this might be the issue. Simply pour a gallon of water down the drain to replenish the P-trap’s water seal. This should restore the barrier against sewer gases. 

Make sure you also frequently use the bathroom or shower to keep it from drying out. This is an easy solution that will help you stop this from happening again.


How A Blocked Or Damaged Vent Pipe Can Cause Sewer Smell

The vent pipe is an essential component of your plumbing system because it lets air in, balances pressure, and stops water from escaping from traps. It usually passes through the top of your house and is connected to your sewer system.



How a blocked or damaged vent pipe can cause sewer smell

A blocked or damaged vent pipe prevents air from moving through your plumbing system as it should. As a result, your P-traps may suck water, creating a vacuum effect that could let sewer gases into your bathroom.


Ways to fix a blocked or damaged vent pipe

If you suspect there is an issue check for any obstructions, like a bird’s nest or debris, like leaves. Also, check for any cracks or breaks in the piping. 

In either case, you should contact a professional to get the vent pipe inspected and fixed.


How A Broken or Damaged Sewer Pipe Can Cause Sewer Smell

A sewer pipe can become damaged or cracked due to various factors, including age, corrosion, tree root intrusion, or ground shifting. Sewage or waste water can leak out of damaged or cracked pipes causing the nasty smell, as well as releasing sewer gas. 

Cracks can also attract pests, like insects and rodents which can compound the issue.


How a broken or damaged sewer pipe can cause sewer smell

If you have concerns about a broken or damaged sewer pipe, contact a licensed plumber. A licensed plumber can scope, the pipe with a plumbing snake. This is a device that has a camera attached to the end and can evaluate the damage. They can then determine if it can be repaired or will require a full replacement. 

While issues do come up,  regular and proper home maintenance can help prevent this from happening.



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How A Leaking Toilet Seal Can Cause Sewer Smell

A vital part that seals the joint between your toilet bowl and the sewage pipe flange is a toilet seal. Sometimes this is referred to as a wax ring or toilet gasket. It sits between the base of the toilet and the floor and is typically made of wax or a wax-like substance.

The seal prevents any sewage or sewer gas from leaking into your bathroom. It forms an airtight and watertight barrier between the bottom of the toilet and the sewer line. 

Mike Holmes looking at the toilet in the bathroom - bathroom renovation and construction

The toilet seal also stabilized the toilet, keeping it securely in place on the floor.


How a leaking toilet seal can cause sewer smell

A compromised toilet seal can cause a sewer smell in your bathroom. This can be due to wear and tear, improper installation, or other factors.

Typically, gas leakage is the cause of the smell. However, in rare cases, a leaking toilet seal can permit wastewater or sewage to seep out from beneath the toilet.



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Ways to fix a leaking toilet seal

If you suspect that this is the culprit, contact a licensed plumber immediately. 

While I always recommend calling the professionals, if you are a seasoned handy-person you can probably do a simple replacement by following these steps:

  1. Turn off the water and flush the toilet to ensure the tank is empty
  2. Disconnect the water supply line from the bottom of the toilet tank
  3. Carefully remove the bolts securing the toilet to the floor and separate the toilet from the flange and old wax ring
  4. Inspect and replace the wax ring. Replace it with a new one if it is damaged. Make sure you centre the new wax ring over the sewer pipe flange
  5. Reinstall the toilet, back onto the new wax ring, align the bolts and gently press down to compress the wax ring and create a seal. Tighten bolts securely.
  6. Reconnect the water supply and check there are no leaks
  7. Test for odours by flushing the toilet a few times



A compromised toilet seal can cause a sewer smell in your bathroom. This can be due to wear and tear, improper installation, or other factors.


How A Build-up of Organic Matter Can Cause Sewer Smell

The build-up of “organic matter” when it comes to plumbing refers to things, such as hair, soap scum, and food particles. Organic debris frequently builds up in bathroom drains, particularly those for sinks, showers, and bathtubs.


How Does The Build-Up Of Organic Matter Cause A Sewer Smell

An accumulation of organic matter in your drains and pipes can lead to plumbing issues, that can cause sewer smells. A clogged drainpipe constricts the flow of water and traps debris creating a blockage which can lead to slow drainage, water backups and sewer gas. As this organic matter starts to decompose or break down it can create foul-smelling gases like hydrogen sulfide. 

This blockage can also prevent sewer gas from venting properly through the vent pipe causing your bathroom to smell.



Ways To Remove Build-Up Of Organic Matter

Again, if you are experiencing any signs relating to sewer smells you should always contact a licensed plumber as they will have the necessary knowledge, experience and equipment to address any issues you have and provide the right solutions. One of a plumber’s most essential tools is a plumbing snake or auger. This tool can go deep into the drainpipe and physically remove hair, and debris. 

However, there are chemical drain cleaners that will help dissolve the blockage but use these with caution as they can be harsh on your plumbing system. A mixture of baking soda and vinegar can also break down the matter, followed by a hot water rinse after a few minutes soak.


Regular maintenance and repair can avoid many problems in your home. However, no bathroom should smell like a sewer. If this happens you have an issue. If you feel this situation is beyond your comfort zone, call the pros. They have the knowledge, experience and equipment to help you find the right solution for you.



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