Toilet Smells Like Sewage When Flushed

I recently contemplated the significance of the modern-day loo and how thankful I am to not have to run to an outhouse or use a bedpan.  However, despite all its underrated benefits, a toilet is not without its faults.  Sometimes they can be a smelly business, and if yours is stinky with each flush, there is likely a solvable problem.

A failing wax ring seal is one of the most common reasons for a sewage-like odor when flushing a toilet.  There are a few other potential culprits, such as a cracked toilet, a toilet that is hardly used, and a clogged drain or vent.  Fixing some may be easy, while others require replacing the loo.

Unfortunately, a good plumber is often relatively expensive, so being able to narrow down the fault yourself could save you a few dollars.  Especially if you are a handy DIYer and can fix the flaw after finding it.  Let’s look at the most common culprits and how to sniff them out.

The Top Reasons Your Toilet Is Smelly

Although probably not the most complicated mechanism in your house, a toilet has several parts, and each piece plays a crucial role.  If one fails, your toilet may stop working as it should. 

There are five reasons your toilet may be struggling to keep the smells outside your bathroom.  Some of these are very easy to fix yourself; others may require getting hold of a plumber.

A Used Toilet Is A Happy Toilet

Right from the get-go, if the smell is coming from a toilet that isn’t regularly used, the first test you should do is flush it daily for a while and see if the issue is resolved.

The fact that surprises many people is that a toilet can only smell better if used regularly.  It’s a brilliant paradox.

The close partner of the wax seal is the water in the toilet bowl.  Or rather, the water inside the “P trap.”  The water you’re used to seeing in the bowl forms an additional barrier between the outer sewage line and your bathroom. 

That same water gets refreshed every time you flush the loo.  However, if a basement or garage toilet is hardly ever used, the water may eventually evaporate.  And when you flush the toilet, the outgoing water opens up the gateway and sends the evil odors rushing in. 

In fact, if the cause is an unused toilet, you may even find it producing odors without any flushing.

a perished wax ring

A Perished Wax Ring

If you have ever had a bathroom remodel, you may have noticed that the toilet’s drainpipe usually gets covered tightly. 

The reason should be apparent, but that pipe is like an evil doorway in a fantasy novel, leading to the odors produced by your entire neighborhood.  Which is why they keep it shut.

So, what about when the toilet is installed?  The proverbial gatekeeper is a combination of the water inside the bowl and the wax ring. 

Traditionally wax rings are made from wax.  However, modern variants include rubberized sealed.  The seal is placed where your toilet is fixed to the drain pipe.  This point is either directly beneath the toilet or at the wall behind the toilet. 

This wax seal provides a water- and air-tight seal.  So, if this seal is perished or worn, it struggles to do its job correctly.  When the toilet is flushed, the inbound odors from the sewage pipeline escape into your bathroom. 

An obvious sign of a worn wax ring is any visible water leakage at the toilet’s base.  Alternatively, if your seal is on the floor, you may experience a slight wobble or “play” in the toilet mounting.

It is a reasonably easy fix if your outlet is behind the toilet.  Just remember to close the water line first and to wear gloves. 

However, suppose the seal is underneath the toilet.  It will require lifting the toilet and resetting it, which may require a plumber if you are not confident.

A Cracked Toilet

Of all the reasons for a smelly toilet, a cracked toilet is obviously the most expensive issue to resolve.  Unfortunately, it requires replacing the entire toilet bowl.

If you see water leaking out your toilet, it could be the wax ring, or it could, in rare cases, be a cracked toilet bowl.  

The best idea is to inspect the toilet and find the exact spot where the water is escaping.  If that spot is below the toilet or drainpipe at the back, it is likely the wax ring.  However, if you find moisture on the outside of the porcelain bowl, then it may be a crack.

Fine cracks may not be obviously visible, so make sure to inspect the toilet carefully.

There’s no easy fix for a cracked bowl, and it’s best to replace the whole thing.  This is quite a task requiring removing the toilet and disassembling it.  The cistern, seat, etc., all need to be reassembled with the new loo and then installed.

A Clogged Drain

If you have had a clogged drain, you absolutely know the horror that it can be. 

A clogged drain will likely produce a smell whether the toilet is being flushed or not.  However, that smell may be amplified with a flush in some instances. 

Toilets can get clogged surprisingly easily by flushing objects that aren’t toilet-friendly, like diapers.  Once blocked, subsequent flushes will accumulate in the pipe between the toilet and clog, making it far easier for odors to escape back into the bathroom.

One sure sign of partial clog is that the toilet bowl fills up with water during a flush cycle.  A complete block may even cause it to spill over. 

Depending on your plumbing setup, a further unfortunate possibility is odors escaping from other connected items like a basin or shower. 

I suggest trying a typical toilet plunger first.  Plungers are extremely effective at clearing blockages, especially from the P trap.  Unfortunately, if the blockage is deeper down the sewage line, you will need to get creative. 

Find the closest inspection hole on the drainpipe outside the house, and then, using a long garden hose, try and clear the block.  A local plumber can help with specialized blockage clearing tools if this doesn’t work.

A Clogged Vent

Even though venting isn’t standardized globally, it is an integral part of how a toilet functions. 

In the USA, especially, venting is standardized and regulated.  Every drain in the house is equipped with a venting pipe that leads up and out of the house.  These vents allow for fresh air intake during drainage, which can cause a slight vacuum. 

They also allow nasty odors to escape through the venting when a toilet is flushed.  If the vent is clogged, that odor finds the path of least resistance, which is into the house.

Clogged vents may be harder to spot, but you should probably get a plumber if you have reached this far down the list and have still not resolved the issue.  They will also check the vents as a probable cause.

If you know where the block is, you can try to remove it with a wire or length of hose.  Alternatively, you could just cut it out and then re-join the pipe when it’s clear. 

A Poorly Installed Toilet Stinks

No one is perfect, and even skilled tradesmen can make mistakes.  And you won’t be happy with a mishap on a toilet installation.

These can come in many forms.  For example, your toilet may be incorrectly set.  Alternatively, the wax seal may not be set correctly, or the drainpipe may not have a sufficient fall to allow the flushed water to run into the drain. 

Some signs may be obvious, like a drain pipe that is visible to “level” (it needs to be angled downward to the outside) or a cracked vent pipe, but some may be harder to spot. 

It may save you a headache to just ask for help and get a plumber to have a look. 


Several reasons could cause a toilet to smell like sewage when flushed.  If a toilet isn’t used regularly, try flushing it daily and see if that improves the situation.  Another common cause is a worn wax ring which keeps the water and odors away from your bathroom floor. 

Alternatively, the issue could be a cracked toilet bowl, a clogged drain or venting pipe, or even a plain old “bab-job-done” by the plumber who installed it.  If you are struggling to find the cause or aren’t confident in fixing the problem, I strongly suggest hiring a plumber to avoid a mess.

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