Plumbing·Drains

How to stop a drain from smelling (2026)

Partially verified

Quick Answer

A smelly drain is usually caused by trapped debris, a dry or faulty trap, biofilm in the pipe, or a venting or sewer problem. Start by working out whether the smell comes from one drain or several, then clean the drain and trap, run water to refill the trap, and check for leaks or loose fittings. If the smell is persistent, affects multiple drains, or smells strongly of sewage, get a plumber to check the trap, venting and waste pipework.

Overview

Drain smells nearly always come from gases or rotting material somewhere in the waste system. In a healthy system, the water sitting in the trap under a sink, shower or bath blocks sewer gases from coming back into the room. If that water seal dries out, leaks away or is disturbed by poor venting, smells can escape. The other common cause is build-up inside the drain itself: soap, grease, hair, food residue and slime can collect just above or below the trap and start to smell even when the drain still empties. The quickest way to narrow it down is to check whether the smell is from one fitting or across the property. One smelly sink usually points to local build-up, a dry trap or a problem with that trap assembly. Several drains smelling at once can point to a venting issue, a blocked waste line, or a wider drainage problem. Clean first, because that fixes many cases and makes diagnosis easier. If cleaning and refilling the trap do not solve it, inspect the trap and nearby pipe joints for leaks or poor sealing. Strong sewage smells, repeated gurgling, slow drainage, or smells that return quickly after cleaning are signs that DIY cleaning is unlikely to be enough.

Who this is for

People troubleshooting bad smells from a sink, basin, bath, shower, floor drain or similar household waste fitting.

What you’ll need

Rubber gloves
Bucket or washing-up bowl
Old cloths or paper towels
Torch
Screwdriver if your drain cover needs one
Drain brush or old bottle brush
Mild detergent or washing-up liquid
Hot water
Bicarbonate of soda and white vinegar if you want a non-caustic cleaning option
Replacement trap washers or seals if you find damaged ones

Before you start

Work out whether the smell is coming from one drain or several. Note any gurgling, slow draining, recent periods of non-use, recent plumbing work, or smells strongest after using another fitting, as these clues help identify a dry trap, blockage or venting issue. If you suspect a cracked pipe, sewage backup, or wastewater leaking into cabinets, stop using that fitting until it has been checked.

Step-by-step

1
Pinpoint which drain is causing the smell
Smell close to each sink, shower, bath and floor drain. Run a little water into each one and note whether the smell gets better, worse or stays the same. Check whether more than one drain smells and whether toilets are also affected.
Why: A single smelly drain usually means local debris, a dry trap or a fault at that fitting. Several affected drains suggest a wider drainage or venting problem.
2
Refill any trap that may have dried out
If the fitting has not been used for a while, run water into it for long enough to restore the water seal in the trap. For floor drains or rarely used fittings, do the same and then monitor whether the smell returns after a period of non-use.
Why: The trap’s water seal blocks sewer gases. If it evaporates away, smells can rise straight through the drain opening.
3
Remove and clean the drain cover and upper waste
Take off the plug, strainer or drain cover if it is removable. Pull out hair, food scraps, soap residue and other visible debris. Scrub the underside of the cover and the inside of the drain opening with detergent and a brush, then flush through with hot water.
Why: A lot of drain odour comes from slimy build-up near the top of the waste, not deep in the pipe. Cleaning this area often solves the smell immediately.
4
Clean the trap if the smell persists
Place a bucket underneath the trap, then carefully loosen and remove the trap if it is designed to be serviceable. Empty it, clean out sludge and rinse the parts. Reassemble it carefully with the existing seals if sound, or replace worn washers or seals. Run water afterwards and check for drips.
Why: The trap is where debris often collects. Cleaning it removes the source of odour and also lets you check whether the trap is damaged or not sealing properly.
5
Treat biofilm inside the waste pipe
If the drain still smells but is not badly blocked, scrub as far into the waste as you can with a flexible brush, then flush with hot water. If you use a drain-cleaning product, follow the manufacturer’s instructions exactly and never mix products.
Why: Bacteria and slime can cling to the pipe walls above and beyond the trap. Physical cleaning helps remove the film instead of only washing over it.
6
Check for leaks, loose joints or trap problems
Use a torch to inspect the trap and nearby waste pipe joints under the sink or basin. Look for dampness, staining, drips, cracked plastic, missing sealing rings, or evidence that the trap is fitted at an odd angle. Also note whether the trap empties noisily or another nearby fitting makes it gurgle.
Why: A trap that leaks, siphons or is incorrectly assembled can lose its water seal and let odours escape even when the drain looks clear.
7
Escalate if there are signs of venting or drain line issues
If multiple drains smell, water drains slowly, there is frequent gurgling, or the smell returns quickly after cleaning, contact a plumber. Explain which fittings are affected and what happens when other appliances or taps are used.
Why: These symptoms point to blocked waste pipework, poor venting or sewer gas problems that usually need proper inspection and repair.

Why this works

Drain odours stop when you either remove the decaying residue that is creating the smell or restore the water and airtight seals that are meant to keep sewer gases inside the drainage system.

Common mistakes to avoid

Pouring cleaner down the drain without first removing hair, grease and slime near the top
Assuming a fresh smell means the problem is fixed when the trap is still dry or leaking
Mixing chemical cleaners or using one straight after another
Overtightening plastic trap fittings and cracking them
Ignoring gurgling sounds, which can point to venting or blockage problems rather than simple dirt

Troubleshooting

Smell from one little-used drain

Refill the trap by running water into the drain. If the smell returns after the fitting sits unused, the trap may be losing its seal through evaporation, leakage or siphoning.

Smell is worst around the plughole but drainage is normal

Clean the drain cover, upper waste and trap thoroughly. This often means biofilm, soap scum, food residue or hair close to the opening.

Drain smells and empties slowly

Remove debris, clean the trap and brush the waste line as far as you can reach. If slow drainage remains, the blockage may be further along the line and need professional clearing.

Several drains smell at the same time

Suspect a wider drainage or venting issue rather than one dirty trap. A plumber should inspect the system, especially if there is gurgling or smells near multiple fittings.

Strong sewage smell even after cleaning

Check for a dry, cracked or leaking trap and for loose waste joints. If no obvious local fault is found, call a plumber promptly because sewer gas may be entering from elsewhere in the system.

Smell gets worse when another sink, bath or appliance drains

This can indicate siphoning or venting issues. A plumber should assess the venting and layout of the waste pipework.

Compare your options

Manual cleaning of drain opening and trap

Best for: Visible debris, food residue, soap scum and hair

Pros: Directly removes the smelly material, low cost, lets you inspect the trap

Cons: Messier than pouring in a product, may not reach build-up further down the pipe

Hot water plus mild detergent

Best for: Light grease and fresh organic residue

Pros: Simple, gentle on most waste systems when used sensibly, useful after scrubbing

Cons: Often not enough on its own for established biofilm or hair

Bicarbonate of soda and vinegar

Best for: Light freshening after physical cleaning

Pros: Easy household option, avoids harsher chemicals

Cons: Not a cure for blockages, dry traps, faulty traps or venting issues

Proprietary drain cleaner

Best for: Cases where the manufacturer states it is suitable for the specific blockage or residue

Pros: Can help break down some deposits

Cons: Must be used exactly as directed, can be hazardous, may not solve the underlying cause, not suitable to mix with anything else

Professional drain and vent inspection

Best for: Repeated smells, multiple affected drains, gurgling, suspected leaks or sewer gas issues

Pros: Finds hidden faults and system-wide problems

Cons: Higher cost than DIY cleaning

Option	Best for	Pros	Cons
Manual cleaning of drain opening and trap	Visible debris, food residue, soap scum and hair	Directly removes the smelly material, low cost, lets you inspect the trap	Messier than pouring in a product, may not reach build-up further down the pipe
Hot water plus mild detergent	Light grease and fresh organic residue	Simple, gentle on most waste systems when used sensibly, useful after scrubbing	Often not enough on its own for established biofilm or hair
Bicarbonate of soda and vinegar	Light freshening after physical cleaning	Easy household option, avoids harsher chemicals	Not a cure for blockages, dry traps, faulty traps or venting issues
Proprietary drain cleaner	Cases where the manufacturer states it is suitable for the specific blockage or residue	Can help break down some deposits	Must be used exactly as directed, can be hazardous, may not solve the underlying cause, not suitable to mix with anything else
Professional drain and vent inspection	Repeated smells, multiple affected drains, gurgling, suspected leaks or sewer gas issues	Finds hidden faults and system-wide problems	Higher cost than DIY cleaning

Alternatives

If you are not comfortable removing a trap, clean the drain opening and use a flexible drain brush as far as you can reach, then monitor whether the smell returns
For rarely used drains, add regular water-running to your maintenance routine to keep the trap seal in place

Pro tips

Clean the underside of sink strainers and pop-up plugs, as slime often hides there
If you remove a trap, take a quick photo first so you can reassemble it correctly
Put a bucket directly under the trap before loosening any fittings
Check inside overflow openings on basins and baths if the smell seems local but the main drain looks clean
A smell that returns quickly after cleaning usually means the cause is not just surface dirt

Safety notes

Wear gloves when clearing drains and handling trapped waste
Never mix drain-cleaning chemicals with each other or with other household cleaners
If a chemical cleaner has already been used, take extra care before opening the trap because splashes can burn
Ventilate the room if there is a strong smell or you are using cleaning products
If you suspect sewer gas from a damaged system, avoid prolonged exposure and arrange repair promptly

Legal & regulatory notes

In many places, drainage and venting work must comply with local building and plumbing rules. If repairs involve altering fixed waste pipework, vents or connections to the foul drainage system, check local requirements or use a qualified plumber.

What this guide does not cover: This guide covers common household drain odours and basic diagnosis. It does not cover major drain excavation, internal sewer inspections, commercial drainage systems, or local code-specific repair methods.

Cost considerations

Simple cleaning is usually low-cost if you already have basic tools. Costs rise if seals or a trap need replacing, and they rise further if the problem turns out to be poor venting, a blocked branch line or a drain defect that needs professional diagnosis.

Prefer to hire a professional?

If this job is beyond a confident DIY — or the work needs to be done by a licensed professional — you can find a verified plumber through Trade Directory (tradedirectory.co.nz), New Zealand's directory of real, verified trade businesses. Compare local tradespeople, read their details and request quotes before you commit.

Find a plumber on Trade Directory

Frequently asked questions

Why does my drain smell even though it is not blocked?+

Because smells often come from slime, soap scum or a dry trap rather than a full blockage. A drain can still empty normally while the upper pipework or trap smells.

Will bleach fix a smelly drain?+

It may mask smells briefly but it does not reliably remove trapped debris or fix a dry or faulty trap. Physical cleaning and checking the trap are usually more effective.

Why does the smell come back after a few days?+

That suggests the underlying cause is still there, such as biofilm further down the waste, a leaking or siphoning trap, or a wider venting or drain problem.

Is a sewage smell from a drain dangerous?+

It can indicate sewer gases entering the room, which should not be ignored. If the smell is strong, persistent or affects several drains, arrange professional inspection.

Can a shower or floor drain smell because it is rarely used?+

Yes. These drains often smell when the trap water evaporates. Running water into them regularly can restore the seal.

Sources & references

Guidance on this page is traced to documented sources. Last checked 24 September 2026.

U.S. Environmental Protection Agency · government
Supports general drainage system care and the importance of maintaining wastewater systems to avoid problems and odours.

Basic drain odour diagnosis and cleaning methods change slowly, though product instructions and local plumbing rules can vary.