You can smell sewage somewhere in the house.
So you check the obvious things.
The toilets are flushing normally. The showers are draining. The sinks aren’t blocked. Nothing is overflowing outside.
But the smell keeps coming back.
This can be one of the more frustrating plumbing problems because a sewer smell doesn’t always come with an obvious blockage.
Sometimes the drainage system is still moving water perfectly well while something else is allowing sewer gases to enter the home.
For homeowners across North Lakes, Mango Hill, Griffin, Murrumba Downs, Kallangur, Narangba and surrounding Moreton Bay suburbs, here are some of the things a plumber may investigate when the source of a sewer smell isn’t obvious.
Can You Have a Sewer Smell Without a Blocked Drain?
Yes.
A blocked drain is only one possible cause of a sewage smell.
Your home’s sanitary plumbing system is designed not only to carry wastewater away, but also to prevent gases from the drainage system entering the living areas of the house.
That protection relies on several components working together, including:
- Water-filled traps
- Drainage vents
- Seals around plumbing fixtures
- Properly installed pipework
- The property’s overflow relief gully
If something goes wrong with one of those systems, you can sometimes smell the problem before you see any other obvious plumbing symptoms.
1. A Trap May Have Dried Out
Under most basins, sinks, showers and other fixtures is a trap designed to hold a small amount of water.
That water creates a barrier between your home and the drainage system.
If the fixture isn’t used for an extended period, the water in the trap can gradually evaporate.
Once the water seal disappears, there may be a direct pathway for unpleasant odours from the drainage system.
This is particularly worth checking in areas that don’t get much use, such as:
- Guest bathrooms
- Spare ensuites
- Floor wastes
- Secondary laundries
- Utility rooms
- Bathrooms in parts of the house that are rarely occupied
Running water through the fixture may refill a dry trap.
But if the smell keeps returning even though the fixture is regularly used, there may be another problem.
2. The Trap May Be Losing Its Water Seal
A trap doesn’t necessarily need to dry out naturally.
Changes in air pressure inside the drainage system can sometimes affect the water sitting inside the trap.
This is where plumbing ventilation becomes important.
The drainage system needs to move air as wastewater travels through the pipes.
If the system isn’t venting correctly, pressure changes can potentially disturb the water seals that are supposed to keep drainage gases out of the home.
You might notice other symptoms such as:
- Gurgling drains
- Toilet water moving when another fixture drains
- Odours appearing after a bath empties
- Smells after the washing machine discharges
- A drain making unusual sucking or bubbling sounds
But sometimes the smell is the main symptom.
3. The Smell Might Not Be Coming From the Drain You Expect
This is what makes sewer odours difficult to diagnose.
The place where you smell it isn’t necessarily the source.
Air movement through the home can carry an odour from one room to another.
It may move through:
- Wall cavities
- Stairwells
- Open-plan living areas
- Ceiling spaces
- Air-conditioning airflow
You might therefore smell sewage strongly in a hallway or living room even though there isn’t a plumbing fixture anywhere nearby.
Rather than focusing exclusively on where the smell is strongest, it is often more useful to work out when it appears.
When Does the Sewer Smell Happen?
Timing can provide valuable clues.
Does the smell appear:
- After somebody showers?
- When the washing machine drains?
- After flushing a toilet?
- When a bath is emptied?
- After heavy rain?
- Only early in the morning?
- When the house has been closed up?
- Only upstairs or downstairs?
A plumber may be able to use those patterns to narrow down which section of the plumbing system needs investigating.
4. A Toilet Seal Can Cause Odours Without an Obvious Leak
The toilet is connected directly to the sanitary drainage system, but the connection itself needs to remain properly sealed.
If that seal is compromised, it may be possible for odours to escape around the toilet connection.
This doesn’t always mean there will be a visible pool of water around the toilet.
If the smell seems concentrated around a bathroom or toilet but the bowl itself looks normal, the fixture connection may be something worth checking.
5. A Plumbing Vent Could Be Involved
You may have noticed plumbing pipes extending through the roof of your house.
These aren’t unfinished drains.
They form part of the ventilation system for the sanitary plumbing.
The venting system helps air move through the drainage network as wastewater flows through it.
If there is a problem with the venting arrangement, the drainage system may not behave the way it was designed to.
Queensland plumbing guidance specifically identifies appropriate ventilation as important for protecting water seals and helping prevent odours from entering habitable areas.
6. What About the Drain Outside the House?
Many Queensland homes have an overflow relief gully, commonly shortened to ORG.
It usually looks like a grated drain outside the house.
Its job is important.
If the sanitary drainage system backs up, the ORG is designed to provide a lower point where sewage can discharge outside rather than backing up through a fixture inside the house.
It should therefore remain accessible and free from landscaping, pot plants or anything else that prevents it operating correctly.
But there is an important point:
An ORG that isn’t overflowing does not prove there is nothing wrong with the plumbing.
If you have an intermittent sewer smell but the ORG looks completely normal, the problem may still be somewhere else in the sanitary plumbing or ventilation system.
7. Could There Be a Partial Drain Blockage?
A drain doesn’t have to be completely blocked before it starts causing trouble.
There can be a restriction while water is still able to pass through the pipe.
Depending on the location and severity of the problem, you might notice:
- Occasional gurgling
- Drains becoming slower over time
- Changes in toilet water levels
- Odours after large amounts of water are discharged
- Problems affecting multiple fixtures
If several fixtures start behaving differently at roughly the same time, it can be a clue that the issue is further down the drainage system rather than at one individual sink or shower.
8. What If the House Is Nearly New?
A newer home isn’t automatically immune from plumbing problems.
If anything, a strange sewer smell in a recently built home can be particularly confusing because homeowners naturally assume the plumbing is too new to have a problem.
But age is only one factor.
Problems can also involve installation, venting, seals, connections or other aspects of the drainage system.
A recent Australian plumbing discussion involved a Brisbane homeowner in a house only around two years old who was experiencing a strong intermittent sewer smell even though the toilets and drains appeared to be working normally.
That is a good example of why sewer odours need to be diagnosed rather than simply assuming the house has a blocked drain.
9. Could It Be a Cracked or Damaged Drain?
If the more obvious causes have been ruled out, the drainage pipework itself may need investigation.
Depending on where the pipe is located, a plumber may use equipment such as a drain camera to inspect inside the system without immediately excavating the property.
A CCTV inspection can help identify issues such as:
- Damaged pipework
- Displaced joints
- Tree-root intrusion
- Foreign objects
- Sections of pipe holding waste
- Other internal drainage problems
The important part is diagnosing the fault before deciding what needs to be repaired.
Should I Pour Drain Cleaner Down It?
If the drains are flowing normally and you don’t actually know where the odour is coming from, pouring chemicals into random drains isn’t much of a diagnostic strategy.
A chemical drain cleaner isn’t going to fix a failed seal, an incorrectly behaving trap, a ventilation issue or damaged pipework.
It is better to understand what is causing the smell first.
What Can I Check Before Calling a Plumber?
If you’re trying to narrow the problem down, there are a few simple observations that can help.
Run water into rarely used fixtures
This can refill a trap that has simply dried out.
Listen for gurgling
Pay attention when toilets flush, baths empty and washing machines discharge.
Work out when the smell appears
Keep track of whether it happens after particular fixtures are used.
Check the outside ORG
Make sure it is accessible and hasn’t been buried, covered or obstructed.
Check whether several fixtures are affected
One smelly drain and several fixtures behaving strangely can point towards very different problems.
Don’t start dismantling sanitary plumbing
Once the basic observations are done, plumbing and drainage work should be left to a licensed plumber.
Why Sewer Smells Can Be Difficult to Diagnose
Some plumbing problems announce themselves very clearly.
A tap leaks.
A toilet blocks.
A pipe bursts.
A sewer smell can be different.
The plumbing may appear to work normally while the smell comes and goes, moves through different parts of the house or only appears under particular conditions.
That is where proper plumbing fault finding becomes important.
Rather than masking the smell, the goal should be to identify how the odour is getting into the home in the first place.
Got a Sewer Smell You Can’t Track Down?
RJT Plumbing & Gas helps homeowners across North Lakes, Mango Hill, Griffin, Murrumba Downs, Kallangur, Narangba and surrounding Moreton Bay areas diagnose difficult plumbing and drainage problems.
If you’ve got a persistent or intermittent sewage smell but can’t find an obvious blockage, we can investigate the plumbing system and help identify where the problem is coming from.
Because when your house smells like a drain, covering it with air freshener isn’t really fixing the problem.
Get in touch with RJT Plumbing & Gas to have the cause properly investigated.
Frequently Asked Questions
Why does my house smell like sewage if nothing is blocked?
A sewer smell does not always mean there is a complete drain blockage. Possible causes can include a dry or disturbed trap, a leaking toilet seal, drainage ventilation problems, a partial blockage or damaged pipework allowing sewer gases to enter the home.
Can drains smell even if they are flowing normally?
Yes. Wastewater can still flow through the drainage system while another issue allows sewer gases to escape. Problems with traps, seals, ventilation or pipe connections may produce odours even when sinks, showers and toilets appear to drain normally.
Can a dry drain trap cause a sewer smell?
Yes. Plumbing traps hold water that creates a barrier between the home and the sanitary drainage system. If a fixture is rarely used, the water can evaporate and allow sewer odours to enter through the drain.
Why does my drain gurgle and smell?
Gurgling combined with sewer odours can indicate that air is not moving normally through the drainage system. Possible causes include a partial blockage, disturbed trap water or a problem with the plumbing ventilation system.
Can a toilet cause a sewer smell without leaking water?
Yes. A compromised seal around the toilet connection can sometimes allow sewer gases to escape without producing an obvious water leak. If the smell is concentrated around a toilet or bathroom, the connection may need to be inspected.
What is an overflow relief gully?
An overflow relief gully, or ORG, is an external plumbing fitting designed to provide a relief point if the sanitary drainage system backs up. It helps reduce the risk of sewage overflowing through fixtures inside the home.
Does a normal overflow relief gully mean my drains are fine?
Not necessarily. An overflow relief gully that is not overflowing only indicates that the drainage system is not currently surcharging at that point. Sewer odours can still be caused by traps, seals, ventilation issues, partial restrictions or damaged pipework elsewhere.
Can a new house still have sewer smells?
Yes. Newer homes can still experience sewer odours if there is an issue with drainage installation, venting, fixture seals, traps or pipe connections. The age of the house does not rule out a plumbing fault.
Should I use drain cleaner if my house smells like sewage?
Drain cleaner is unlikely to help if the problem is caused by a dry trap, failed seal, ventilation issue or damaged pipework. If the drains are flowing normally and the source of the smell is unclear, it is better to identify the cause before using chemicals.
When should I call a plumber about a sewer smell?
Call a licensed plumber if the smell is persistent, keeps returning, is accompanied by gurgling or slow drainage, affects several fixtures, or cannot be traced to a simple dry trap. A plumber can inspect the drainage system and determine how the odour is entering the home.
