Why Does My Drain Smell? Common Causes and Simple Solutions

An unpleasant smell coming from a sink, shower or outside drain is more than an inconvenience. It can indicate trapped food, hair, stagnant water or a blockage developing inside the drainage system.

Some drain smells can be resolved with basic cleaning. However, persistent sewage odours, gurgling sounds or smells affecting several fixtures may indicate a deeper problem that requires professional investigation.

What Causes a Drain to Smell?

The source of the smell can vary depending on which drain is affected.

Food and grease in kitchen drains

Food particles, cooking fat and grease can collect inside kitchen waste pipes. Bacteria begin to break down this material, creating an unpleasant, rotten smell.

Even when cooking oil enters a drain as a liquid, it can cool and solidify inside the pipe. Additional food waste then sticks to the buildup.

Hair and soap in bathroom drains

Hair, soap, toothpaste and other bathroom products can collect around the plughole and inside the waste pipe. This creates an organic buildup where bacteria can grow.

A bathroom sink or shower may begin to smell before it becomes completely blocked.

A dirty sink overflow

The overflow opening near the top of a bathroom sink can collect soap, toothpaste and stagnant water. Customers may clean the main plughole but overlook this hidden area.

If the smell appears when the tap is running, the overflow may need cleaning.

A dry U-bend

The curved pipe underneath a sink holds a small amount of water. This creates a barrier that prevents gases from travelling back through the drainage system.

If a sink, shower or floor drain has not been used for some time, this water may evaporate and allow unpleasant smells into the room.

A blocked or damaged drain

Persistent sewage smells can indicate a deeper obstruction, cracked pipe, loose connection or ventilation problem. These issues normally require professional drainage equipment to diagnose.

How to Identify Where the Smell Is Coming From

Try to determine whether the odour comes from one fixture or affects several parts of the property.

Ask the following questions:

Does the smell come from the kitchen or bathroom?
Is only one drain affected?
Does the smell become stronger when water runs?
Is the drain emptying slowly?
Can you hear gurgling noises?
Has the drain been unused for several weeks?
Is an outside drain overflowing?
Does the smell resemble sewage or rotten eggs?

If several drains smell or drain slowly simultaneously, the problem may be located in a shared or main drainage pipe.

How to Clean a Smelly Drain Safely

Wear suitable gloves before cleaning a drain and keep children and pets away from the area.

Remove visible debris

Remove the stopper or drain cover and check for accessible hair, food or soap residue. Use a plastic drain-cleaning tool to lift hair from bathroom plugholes.

Place the debris in a bin rather than washing it further down the pipe.

Clean the stopper and strainer

Wash the sink stopper or kitchen strainer with warm water and washing-up liquid. Pay particular attention to its underside, where residue often collects.

Flush with hot tap water

Hot tap water may help remove light soap and grease deposits. Avoid using boiling water if your drainage system contains PVC pipes, rubber seals or older joints.

Stop adding water if it begins to collect rather than drain away.

Clean the sink overflow

Use a small flexible cleaning brush to carefully clean the overflow opening. Avoid forcing rigid objects into the opening, as they may become stuck or damage the fitting.

Refill a dry trap

If a sink or drain has not been used recently, run the tap for 20–30 seconds. This should refill the U-bend and restore the water barrier.

If the smell returns quickly, there may be a leaking trap, damaged fitting or ventilation issue.

Check the U-bend

If the smell remains, debris may be trapped inside the U-bend underneath the sink.

Place a bucket and towel beneath the pipe before carefully removing it. Clean the trap and ensure its seals are correctly positioned when it is reassembled.

If the fittings are corroded, difficult to move or unfamiliar, contact a professional instead.

Should You Use Chemical Drain Cleaner?

Chemical cleaners may temporarily cover a smell without removing its underlying cause. Repeated use can affect certain pipes, seals and finishes.

Never mix drain cleaner with bleach, ammonia, acids or other household products. Mixing chemicals can create dangerous fumes.

If you have already used a chemical product, tell the drainage engineer before they begin work.

Why Does the Smell Keep Returning?

A recurring smell may be caused by:

A partial blockage deeper inside the pipe
Fat and grease buildup
A leaking or incorrectly fitted U-bend
A blocked drainage vent
Tree roots entering underground pipework
Cracked or damaged pipes
A blockage in a shared drain or sewer
Poorly installed waste pipes

Cleaning the plughole may provide temporary relief, but it will not repair damaged pipework or clear a deeper obstruction.

A CCTV drain survey can inspect the inside of the pipe and identify blockages, cracks, displaced joints, tree roots and other structural problems.

When Should You Call a Drainage Professional?

Contact Better Drains if:

The smell resembles sewage
Several drains are affected
The smell repeatedly returns
Water is draining slowly
You hear persistent gurgling
Wastewater is backing up
An outside drain is overflowing
You suspect a leak or damaged pipe
Cleaning the plughole and trap has not helped

Persistent sewage smells should not be ignored, particularly when accompanied by slow drainage or wastewater backing up.

How Can You Prevent Smelly Drains?

Simple maintenance can reduce future smells:

Use strainers in kitchen sinks
Fit hair catchers in showers and baths
Never pour cooking fat down the sink
Remove food waste before washing dishes
Clean sink stoppers regularly
Run water into rarely used drains
Only flush toilet paper
Investigate slow drainage promptly

Need Help With a Smelly Drain?

If cleaning the plughole and trap has not removed the smell, the problem may be deeper inside the drainage system.

Better Drains can investigate persistent smells using professional drain-clearance equipment and CCTV inspections. Contact our team to identify the cause and find the appropriate solution.

Frequently Asked Questions

Why does my sink smell like rotten eggs?

A rotten-egg smell may be caused by trapped organic material, stagnant water or drainage gases. Persistent odours should be professionally investigated.

Why does my drain smell when I run the tap?

Running water may disturb residue inside the waste pipe or sink overflow. It can also displace air when a partial blockage is present.

Can a blocked drain cause a bad smell?

Yes. Food, grease, hair and other waste trapped inside a pipe can produce unpleasant smells as it breaks down.

Why does an unused drain smell?

The water inside its trap may have evaporated, allowing drainage gases to enter the property. Running water may refill the trap.

Will cleaning the plughole remove the smell?

It may resolve smells caused by surface buildup. If the odour returns, there may be a deeper blockage, leaking trap or damaged drainage pipe.