Why Does My Drain Smell? Common Causes and Solutions

Have you noticed an unpleasant smell coming from your kitchen sink, bathroom or laundry drain?

Drain odours are a common household plumbing concern, and while some have relatively simple causes, others can indicate a problem within your plumbing or drainage system.

Whether it's a musty smell coming from the bathroom, an unpleasant odour around the kitchen sink or a persistent sewage smell, understanding what might be causing it is the first step towards finding a solution.

At Onboard Plumbing & Gas, we help homeowners across Adelaide's southern suburbs identify and resolve plumbing and drainage problems, including blocked drains, leaking pipes and unpleasant drain odours.

Here's what could be causing that smell and when it's worth calling a licensed plumber.

1. Food, Grease and Debris Build-Up

Kitchen sinks are particularly prone to unpleasant smells because of what regularly goes down the drain.

Small amounts of food, grease, oils and other debris can accumulate inside waste pipes over time.

As organic material breaks down, it can produce unpleasant odours that become noticeable around the sink.

Common signs include:

• An unpleasant smell near the kitchen sink

• Water draining more slowly than usual

• Gurgling noises when water drains

• Odours that return shortly after cleaning

Avoid pouring cooking oils and grease down the sink, and use a sink strainer to catch food scraps.

If the smell persists or drainage becomes slow, there may be a build-up or blockage that requires professional attention.

2. A Dry Drain Trap

Have you noticed a smell coming from a bathroom, laundry or floor drain that doesn't get used very often?

One possible cause is a dry drain trap.

Many plumbing fixtures have a trap designed to hold a small amount of water. This water acts as a barrier that helps prevent sewer gases from entering your home.

When a drain isn't used regularly, the water in the trap can evaporate, allowing unpleasant odours to escape.

This can sometimes happen in:

• Spare bathrooms

• Guest toilets

• Laundry floor wastes

• Showers that are rarely used

• Other infrequently used fixtures

If the drain is accessible and safe to use, running some clean water into it may help restore the water seal.

However, if the smell continues or returns regularly, further investigation may be needed.

3. A Blocked or Partially Blocked Drain

Blocked drains don't always result in water backing up immediately.

Sometimes a blockage develops gradually, allowing water to continue flowing while debris collects inside the pipe.

Over time, this trapped material can contribute to unpleasant odours.

Warning signs of a possible blocked drain include:

• Water draining slowly

• Gurgling sounds

• Recurring unpleasant smells

• Water backing up into a sink, shower or floor drain

• Several fixtures experiencing drainage problems

Common causes of blockages include grease, hair, soap residue, foreign objects and tree-root intrusion.

If multiple drains are affected or the problem keeps returning, it's worth arranging a professional plumbing inspection.

At Onboard Plumbing & Gas, we assist with blocked drains and drainage problems throughout Adelaide's southern suburbs.

4. Plumbing Ventilation Problems

Your home's drainage system includes ventilation designed to help maintain appropriate air pressure and allow wastewater to flow correctly.

If the plumbing ventilation system isn't functioning as intended, it may contribute to drainage problems or unpleasant smells.

Possible symptoms include:

• Gurgling noises from fixtures

• Water being drawn out of drain traps

• Unpleasant odours near sinks, toilets or floor drains

• Drainage problems affecting multiple fixtures

Ventilation problems can have several causes and aren't always easy to identify without a professional inspection.

A licensed plumber can assess the drainage system and determine whether an issue with ventilation, a trap or another component is contributing to the smell.

5. Problems With Seals, Connections or Drainage Pipes

Sometimes the source of a drain smell isn't trapped debris or a blockage.

Damaged seals, loose fittings, deteriorating pipework or faulty plumbing connections may allow unpleasant gases or wastewater odours to escape.

For example, a faulty toilet seal may cause a sewage smell around the base of the toilet, even if the toilet appears to flush normally.

Other warning signs may include:

• Persistent odours around a plumbing fixture

• Dampness or water staining

• Visible leaks

• Recurring smells despite regular cleaning

These problems generally require professional assessment to identify the cause and carry out the appropriate repair.

6. Outdoor Drainage Problems

Unpleasant smells aren't always limited to indoor plumbing.

Outdoor drains, inspection points and sewer connections can also develop odours when there is a blockage, damaged pipework or another drainage issue.

You may notice smells around outdoor plumbing, garden areas or drainage points.

If an outdoor drain is overflowing or producing a persistent sewage smell, avoid direct contact with wastewater and arrange professional assistance.

In some situations, a CCTV drain inspection may be recommended to investigate recurring blockages or identify possible pipe damage.

Can You Fix a Smelly Drain Yourself?

Some basic maintenance may help when a drain smell has a simple cause.

However, it's important to avoid methods that could damage your plumbing or create safety risks.

A few safe things to consider include:

Remove visible debris: If accessible, clear hair or food scraps from strainers and drain openings without dismantling plumbing.

Run water into rarely used drains: This may help restore the water seal in a dry trap.

Keep grease out of kitchen sinks: Dispose of cooking oils and fats appropriately rather than pouring them down the drain.

Clean accessible strainers and waste covers: Regular cleaning can help prevent organic material from accumulating.

Monitor drainage performance: Take note of slow drainage, gurgling or smells that keep returning.

Avoid using harsh chemical drain cleaners as a regular solution, particularly when the cause of the problem is unknown. These products may create safety risks and may not address the underlying issue.

If the smell persists, it's best to have the drainage system checked rather than repeatedly trying temporary fixes.

When Should You Call a Plumber for a Smelly Drain?

An occasional odour may have a relatively simple explanation, but some symptoms suggest a plumbing problem that shouldn't be ignored.

Consider contacting a licensed plumber if:

• The smell persists or regularly returns

• Several drains are affected

• Water is draining slowly or backing up

• You notice gurgling sounds

• There are signs of leaking wastewater

• The smell is particularly strong or resembles sewage

• Previous attempts to resolve the problem haven't worked

Persistent smells can sometimes be associated with blockages, drainage faults or damaged plumbing connections.

A professional inspection can help identify the cause and determine the most appropriate solution.

Frequently Asked Questions About Smelly Drains

Why does my bathroom drain smell like sewage?

A sewage smell from a bathroom drain may be caused by a dry trap, drainage blockage, ventilation issue or faulty plumbing connection.

If running water into a rarely used drain doesn't resolve the smell, professional assessment may be needed.

Why does my kitchen sink smell even after cleaning it?

Cleaning the sink itself doesn't necessarily remove material that has accumulated further inside the waste pipe.

Grease, food debris and other organic material may continue to produce odours even when the visible sink is clean.

Persistent smells may indicate a build-up or drainage issue that needs attention.

Can a blocked drain cause a bad smell?

Yes. Blockages can trap organic material and wastewater, which may contribute to unpleasant odours as the material breaks down.

Other signs may include slow drainage, gurgling or water backing up.

Is a smelly drain always a serious plumbing problem?

Not necessarily. Some drain odours have simple causes, such as a dry trap in a rarely used bathroom.

However, persistent sewage smells, recurring blockages or drainage problems should be investigated to rule out more significant issues.

Can tree roots cause smelly drains?

Yes. Tree roots can enter damaged or vulnerable underground drainage pipes and contribute to blockages.

This may lead to slow drainage, recurring blockages and unpleasant odours.

A CCTV drain inspection may help identify the location and extent of a suspected problem.

Should I use chemical drain cleaner to remove the smell?

Chemical drain cleaners are not always appropriate and may not resolve the underlying cause of the smell.

Some products can also pose safety risks or cause damage if used incorrectly.

If the problem keeps returning, a licensed plumber can investigate and recommend a suitable solution.

Need Help With Smelly or Blocked Drains in Adelaide's Southern Suburbs?

If an unpleasant drain smell keeps returning, it's worth finding out what's causing it rather than simply covering it up.

At Onboard Plumbing & Gas, we provide professional plumbing and drainage services across Seaford, Morphett Vale, Christies Beach, Port Noarlunga, Aldinga, Woodcroft, Reynella and surrounding southern Adelaide suburbs.

Whether you're dealing with a blocked sink, slow-draining shower, unpleasant sewer odours or recurring drainage problems, Luke can help investigate the issue and recommend a practical solution.

Need a reliable local plumber? Get in touch with Onboard Plumbing & Gas.