Few home issues are more unpleasant than the smell of sewage drifting through a property. It’s not only uncomfortable to live with but also often a sign that something is wrong with the drainage system. Persistent odours may point to underlying faults that, if ignored, could lead to blockages, leaks, or even structural damage.

Sewage smells are not always constant and can vary depending on time of day, weather, or water usage. This makes them difficult to track down without a proper investigation. Understanding the likely causes and how to resolve them is essential for maintaining a safe and hygienic home.

Common Causes of Sewage Smells

The source of a sewage smell isn’t always where it seems. It may be coming from inside the home, from external drains, or from below ground level.

Some of the most common causes include:

• Dry or faulty traps – Every sink, shower, and toilet uses a U-bend to hold water and block sewer gases. If the trap dries out or is damaged, smells can travel back up into the room.
• Blocked or partially blocked vents – Soil stacks must vent air to equalise pressure. If the vent is blocked, air may escape through internal drains.
• Loose pipe joints – Particularly in older systems or those that have been modified, unsealed joints can allow gases to escape.
• External drain blockages – Waste build-up in outdoor gullies or manholes can cause smells to rise into the home.
• Cracked underground pipes – These can release gases into the soil or cavity spaces, often creating smells inside basements or lower ground floors.

Where to Start Looking

To diagnose the source of the smell, consider when and where it occurs:

• Only in bathrooms or kitchens? Check traps, waste pipes, and connections.
• Worse after heavy rain? The problem may be linked to external drains or poor surface water management.
• Concentrated near walls or floors? This could indicate a leaking underground pipe or a venting issue.
• Intermittent or seasonal? Environmental conditions may be affecting air pressure in the system.

It’s worth running water through all fixtures to refill traps and see if the smell improves temporarily.

Short-Term Fixes That Might Help

In some cases, simple steps can reduce or eliminate smells:

• Run water through all drains regularly – especially in guest bathrooms or unused sinks.
• Flush toilets that aren’t used often
  
• Check outside gullies for trapped debris and rinse with clean water
• Seal any visible pipe joints that appear loose or corroded

If these steps don’t make a difference or the smell returns quickly, a deeper issue is likely.

How Professionals Diagnose Persistent Drain Smells

When DIY methods don’t work, it’s time for a full system inspection. Drainage engineers use several advanced tools to find the source of persistent smells:

• CCTV drain surveys – A small camera is fed through your drainage system to check for cracks, displaced joints, or trapped waste.
• Smoke testing – A non-toxic smoke is pumped through the system to reveal where air or gas may be escaping. This is especially useful for internal venting issues.
• Odour tracing dye – In some cases, coloured dye can be added to the system to help identify leaks or incorrect connections.
• Air pressure testing – Used to check that vent stacks and traps are holding pressure and functioning correctly.

These methods allow for accurate diagnosis with minimal disruption to the property.

Repair Options Based on the Cause

Once the issue has been identified, repairs can range from minor fixes to full drainage upgrades:

• Replacing or resealing faulty pipe joints
• Cleaning and restoring vent pipes
• Clearing and reconfiguring external drains and gullies
• Installing air admittance valves where traditional venting isn’t viable
• Relining or replacing cracked underground pipe sections

Qualified drainage professionals will explain the most suitable approach based on your home’s layout and drainage design.

To address the issue properly and prevent recurrence, it’s best to work with a team that can both diagnose and resolve the issue. Services that resolve persistent sewage smells typically include both inspection and repair under one callout.

Prevention Tips to Keep Smells from Returning

Once resolved, there are a few habits and upgrades that can help reduce the risk of future odours:

• Pour a cup of water down unused drains every few weeks to keep traps sealed
• Regularly inspect visible waste pipes for cracks or corrosion
• Avoid pouring fats, oils, or food waste down the sink
• Install trap guards in showers and sinks to prevent hair and soap buildup
• Schedule a professional drain inspection every few years in older properties

Being proactive with maintenance is the best way to stop a minor smell from becoming a costly repair later.

Sewage Smells Are a Sign Worth Investigating

Unpleasant odours around the home can be more than just a nuisance. They often indicate hidden drainage faults that need attention sooner rather than later. While air fresheners and cleaning might mask the symptoms, they won’t resolve the root cause.

If smells are persistent, unexplained, or worsening, professional support is the safest and most effective route. With the right equipment and expertise, a drainage specialist can identify the issue, fix it thoroughly, and help you avoid a repeat occurrence.

Book an inspection with trusted professionals who can quickly and safely resolve persistent sewage smells for good.