Can blocked drains cause bad smells in my home, and how do I get rid of them?

Yes. Blocked drains are one of the most common causes of unpleasant smells inside Australian homes. When food scraps, grease, hair, soap residue, leaves, or other organic material become trapped inside pipes, they begin to decompose and encourage bacterial growth. This process creates foul-smelling gases that can travel back through your plumbing system and into your home. The most effective way to get rid of these smells is to identify and remove the underlying blockage rather than simply masking the odour.

Persistent drain odours should never be ignored. While some smells are caused by minor build-up that can be resolved with simple maintenance, others may indicate a blocked sewer, damaged pipe, or ventilation problem requiring professional attention. Understanding the source of the smell helps prevent more serious plumbing issues and protects your home’s hygiene and safety. To better understand why drainage problems occur, read our guide on What are the most common causes of blocked drains in homes? 

If unpleasant smells are accompanied by slow drainage, gurgling pipes, or recurring blockages, professional drain cleaning may be required to restore your plumbing system. Learn more about MPJ Plumbing’s professional blocked drain services. 

Why do blocked drains smell?

Unpleasant drain odours develop when waste becomes trapped inside your plumbing system instead of flowing freely into the sewer.

Over time, this trapped material breaks down, allowing bacteria to multiply and release gases with strong, unpleasant smells.

Common contributors include:

Organic waste decomposition

Food scraps, grease, soap residue, hair and other organic matter naturally decompose. As bacteria feed on this material, they release sulphur compounds and other gases responsible for the familiar rotten smell.

Grease and food waste

Kitchen sinks frequently accumulate cooking oils, fats and grease. These substances harden inside pipes and trap additional food particles, creating an ideal environment for bacterial growth.

Hair and soap residue

Bathroom drains commonly collect hair, soap scum and toothpaste. Together they form sticky blockages known as biofilm, which produces persistent plumbing odours.

Standing water

Partial blockages slow water movement, allowing stagnant water to remain inside pipes. Standing water quickly develops unpleasant smells as bacteria multiply.

Sewer gases

A blocked sewer or damaged pipe can allow sewer gases to escape into your home. These gases often produce a strong sewage smell and may indicate a more serious plumbing issue.

Common causes of bad smells coming from drains

Different parts of your home can develop different types of plumbing odours depending on the waste travelling through the pipes.

Kitchen drains

Kitchen drains are among the most common sources of smelly drains because they regularly receive:

• Grease and cooking oils
• Fat
• Food scraps
• Coffee grounds
• Rice and pasta
• Dairy products

Even with a sink strainer, small particles gradually accumulate inside pipes.

Bathroom drains

Bathrooms commonly develop drain odour from:

• Hair
• Soap scum
• Toothpaste
• Shaving cream
• Biofilm

Shower and basin drains often smell long before they become completely blocked.

Laundry drains

Laundry drains collect:

• Lint
• Detergent residue
• Dirt
• Pet hair
• Fabric fibres

These materials combine to restrict water flow and create unpleasant odours.

Outdoor drains

Outdoor drains frequently become blocked by:

• Leaves
• Grass clippings
• Mud
• Garden debris
• Tree roots

Organic material decomposes quickly, producing noticeable smells around the property.

Sewer drains

A blocked sewer can create the strongest sewage smell inside or outside your home.

Common causes include:

• Tree root intrusion
• Collapsed pipes
• Heavy grease build-up
• Foreign objects
• Ageing pipework

How to identify which drain is causing the smell

Finding the source of bad smells from drains is often straightforward if you inspect each fixture individually.

Check sink drains

Run water through each kitchen and bathroom sink.

If one sink produces a stronger smell than others, it is likely where waste has accumulated.

Inspect shower drains

Remove the drain cover and check for:

• Hair build-up
• Soap residue
• Visible debris

Clean the strainer before testing again.

Examine floor wastes

Laundry rooms and bathrooms often contain floor wastes.

If these drains are rarely used, the water inside the trap may evaporate, allowing sewer gases to enter the room.

Simply pouring water into the drain can sometimes restore the water seal.

Inspect toilets

A sewage smell around the toilet may indicate:

• A blocked sewer
• Damaged seals
• Ventilation issues

This should be professionally assessed if the smell persists.

Check outdoor inspection openings

Strong odours outside inspection points can indicate:

• Partial sewer blockage
• Tree root intrusion
• Damaged sewer lines

These situations often require specialised equipment to diagnose accurately.

When bad smells indicate a more serious plumbing problem

Not every drain odour is a plumbing emergency, but some warning signs suggest a more significant issue.

These include:

• Slow draining sinks
• Gurgling noises
• Multiple fixtures draining slowly
• Water backing up into showers or floor wastes
• Sewage smell throughout the home
• Overflowing outdoor drains

These symptoms often indicate blocked drains affecting the main sewer line rather than an isolated fixture.

If you’ve already noticed slow drainage before the smells developed, read our guide on What are the early warning signs of a blocked drain before it becomes a major plumbing problem to learn which warning signs homeowners should never ignore. 

Likewise, if sewage has already started backing up into your property, immediate professional assistance is recommended to minimise health risks and property damage.

Safe ways to reduce drain odours

While permanent solutions require removing the blockage itself, homeowners can safely reduce minor drain odours with regular maintenance.

Flush with hot water

Running hot water through kitchen drains helps soften grease before it hardens.

Avoid boiling water if you have PVC pipework.

Clean drain strainers

Regularly remove:

• Hair
• Food scraps
• Soap residue

This simple habit significantly reduces bacterial growth.

Maintain water traps

Unused floor wastes can dry out.

Pour fresh water into these drains every few weeks to maintain the protective water seal.

Improve ventilation

Bathrooms with poor ventilation allow moisture and odours to linger longer.

Use exhaust fans after showers to improve airflow.

Avoid pouring these into drains

Do not dispose of:

• Cooking oils
• Fat
• Grease
• Coffee grounds
• Paint
• Chemicals
• Wet wipes
• Sanitary products

These materials contribute to future blocked drains and unpleasant smells.

Are chemical drain cleaners a good solution?

Chemical drain cleaners may temporarily reduce some blockages, but they rarely solve the underlying problem.

Potential drawbacks include:

• Damage to older pipes
• Corrosion of plumbing components
• Environmental impacts
• Temporary rather than permanent results
• Increased difficulty during professional repairs

If smells return shortly after using chemical products, professional diagnosis is usually the better long-term solution.

A CCTV drain inspection can reveal exactly what is causing the blockage without unnecessary guesswork.

How plumbers permanently eliminate smelly blocked drains

Professional plumbers focus on eliminating the cause rather than masking the smell.

Depending on the diagnosis, solutions may include:

CCTV drain inspection

Specialised drain cameras identify:

• Grease build-up
• Tree roots
• Broken pipes
• Misaligned joints
• Foreign objects

This allows targeted repairs without unnecessary excavation.

High-pressure water jetting

High-pressure water jetting removes:

• Grease
• Biofilm
• Sludge
• Tree root fragments
• Organic waste

Unlike temporary clearing methods, it thoroughly cleans pipe walls.

Tree root removal

Roots invading underground pipes require specialised cutting equipment followed by pipe assessment.

Pipe repairs

Cracked or collapsed pipes may require excavation or trenchless repair methods.

Pipe relining

Where suitable, pipe relining repairs damaged sewer pipes internally without extensive digging.

Preventative maintenance

Regular inspections and drain maintenance help identify small issues before they become major blockages or produce persistent odours.

How to prevent blocked drains from smelling again

The best way to avoid recurring drain odour is through ongoing maintenance.

Good habits include:

• Clean sink strainers weekly.
• Never pour grease down kitchen sinks.
• Dispose of food scraps in the bin.
• Flush little-used floor wastes regularly.
• Keep outdoor drains clear of leaves.
• Schedule periodic professional drain cleaning.
• Arrange CCTV inspections if blockages repeatedly occur.
• Address slow drainage before complete blockages develop.

Preventative maintenance is generally far less expensive than repairing a blocked sewer or replacing damaged underground pipes.

Conclusion

Bad smells coming from your plumbing are often an early warning sign that blocked drains are developing somewhere within your drainage system. While minor odours may be caused by accumulated organic material or dried water traps, persistent sewer smells, slow drainage, gurgling pipes or recurring blockages often indicate more serious issues that should be professionally investigated.

Rather than masking unpleasant smells with chemical cleaners or air fresheners, identifying and removing the underlying cause provides the safest and most effective long-term solution.

If you’re experiencing persistent drain odours, recurring blocked drains, or signs of a blocked sewer, MPJ Plumbing can help with professional drain cleaning, CCTV drain inspections, high-pressure water jetting, and long-term drainage solutions to keep your plumbing system flowing freely.

Frequently Asked Questions

1. Why does my kitchen sink smell even when it drains normally?

Grease, food residue and biofilm can build up inside pipe walls before causing a noticeable blockage. These deposits often produce unpleasant smells even while water continues to drain.

2. Can a dry floor waste cause a sewer smell?

Yes. If the water trap dries out, sewer gases can enter your home. Pouring water into the drain usually restores the seal unless another plumbing issue is present.

3. Is a sewage smell in my bathroom dangerous?

Sewer gases can contain harmful compounds and should not be ignored. Persistent sewage odours should be inspected by a licensed plumber.

4. Why do drain smells return after using a chemical cleaner?

Chemical cleaners may remove a small portion of the blockage but often leave grease, roots or debris behind. Without addressing the underlying cause, smells usually return.

5. Can heavy rain make blocked drains smell worse?

Yes. Stormwater entering partially blocked drains can disturb trapped organic material and sewer gases, making odours more noticeable.

6. How often should drains be professionally cleaned?

Homes with mature trees, older pipework or recurring drainage issues may benefit from professional drain cleaning every one to two years, while other properties may require it less frequently.

7. What is the fastest way to find the source of a drain odour?

Start by checking each sink, shower, floor waste and outdoor inspection point individually. If the source isn’t obvious, a CCTV drain inspection can quickly identify hidden blockages or pipe damage.

Continue reading this series:

• How can I prevent blocked drains in my kitchen, bathroom, and outdoor drains?
• Can tree roots damage underground pipes, and how can they be removed?
• Why do blocked drains keep coming back, and how can they be permanently fixed?

Authoritative resources

• NSW Health – https://www.health.nsw.gov.au/
• Sydney Water – https://www.sydneywater.com.au/
• Water Services Association of Australia (WSAA) – https://www.wsaa.asn.au/