How to Clean Smelly Drains in Your Home

Q: Can a smelly drain be a sign that your P-trap is incorrectly sized or installed, rather than just dried out?

Absolutely — an undersized or poorly fitted P-trap won&#39;t hold an adequate water seal even with regular use, meaning sewer gas escapes continuously rather than only when the fixture sits idle. If flushing the drain with water doesn&#39;t resolve the smell within a day or two, it&#39;s worth having a licensed plumber inspect the trap configuration itself.

Q: Is it safe to use bicarb and vinegar in drains connected to a septic system?

Yes, in the quantities described here it&#39;s fine — the reaction neutralises before reaching the tank and won&#39;t disrupt the bacterial activity your septic system depends on. Avoid harsh chemical drain cleaners if you&#39;re on septic, as those can genuinely damage the microbial balance.

Nothing is worse than stepping into your bathroom and immediately getting hit by that noxious, musty, slightly rotting smell that seems to seep up from the drain. No matter how many scented candles you light, you'll continue to smell something gross coming up the drain as long as you don't get to the bottom of what's happening below the drain cover.

A practical tutorial on cleaning smelly shower and sink drains, covering common causes of drain odour and step-by-step methods to eliminate bad smells effectively.
Video Credit: HouseBarons

Why Your Drains Smell (and What's Actually Causing It)

The different smells in your drains can actually indicate very different things, so knowing what you're dealing with can help you get to the bottom of how best to fix that smell.

Bathroom drains – shower, bath, and basin – almost always smell because of hair, soap scum and a slimy substance growing on the walls of the drain over time. It's pretty gross to think about, but there you have it. In the kitchen, drain smells are a different matter. They smell because of decomposing food and grease that build up inside the drain.

The other possible culprit is a dried-out P-trap, the curved section of pipe directly underneath your drain that's designed to hold a small amount of water to create a seal that prevents sewer gas from coming up into your home. If you don't use a drain regularly (a guest bathroom, for example), that water evaporates, the seal fails, and sewer gas can rise into your home. Sewer gas can contain hydrogen sulphide, which is both unpleasant and potentially harmful at higher concentrations. Australian building codes also require bathroom exhaust fans to move at least 25 L/s (NCC 2025, ABCB Housing Provisions, Part 10.8) of air to manage moisture and odour — so if your exhaust fan is undersized or broken, that's making everything worse.

Once you've identified the type of build-up or obstruction that's causing the smell, you'll need to gather together all of your equipment and cleaning supplies before you start.

Bicarb soda, white vinegar, yellow rubber gloves, drain snake and bucket on marble benchtop beside white sink

What You'll Need Before You Start

There's good news: there's no need to trek to a plumbing supply shop to learn how to clean smelly drains. Most of what you need is probably already in your pantry or can be purchased in one trip to a hardware store for under a few dollars.

You'll want:

• a box of bicarb soda (about $2)

• a bottle of white vinegar ($3 for a 750ml bottle)

• rubber gloves

• a bucket

• a drain tool such as a zip-it drain cleaning tool or drain snake (these are $5 to $15, depending on the type)

Regular hot tap water should do just as well for flushing down any remaining debris. Boiled kettle water is too hot for PVC and can soften the joints over time.

And this cannot be overstated: never mix bleach with vinegar, or any ammonia-based cleaner for that matter. The chemical reaction can produce toxic chloramine gas. Stick to the bicarb and vinegar method, or use an enzyme-based cleaner — not both at the same time. Any replacement drains or drain covers you purchase need to be WaterMark certified, which is the national standard (and mandatory) for all plumbing and drainage products in Australia. With everything laid out and safety precautions in mind, you're ready to go through the full cleaning process from beginning to end.

Gloved hands pouring white powder into white kitchen sink drain

Step-by-Step: How to Clean Smelly Drains

Take the drain cover off, give it a hot-water rinse, and scrub any visible hair or soap scum with an old toothbrush. Pour half a cup of bicarb soda down the drain and follow with half a cup of white vinegar. It will bubble — that's what's supposed to happen. Leave it for 15 minutes while the reaction works on the biofilm lining the pipe walls, then flush through with a few litres of the hottest tap water you can run.

If it still smells, or the water is slow to drain, feed a zip-it tool or drain snake down the opening to physically pull out whatever is sitting in the pipe. It'll probably gross you out, but do it anyway. Stick to this routine once a month and you'll largely stay on top of how to clean smelly drains before problems take hold.

Hand pulling clump of wet hair from white shower drain

Bath Drains and Plugs: How to Clear Them Out

Bath drains warrant their own explanation, especially when it comes to the bathtub plug itself.

Australians can generally expect one of three types of plugs: a push-pull stopper, a lift-and-turn stopper, or a pop-up stopper. If your bathtub plug has developed a build-up of hair and soap scum around the base, simply unscrew or unclip it from the drain flange, clean it, and reinstall. If you find your bath drain plug stuck in a closed position, grip the cap and twist firmly to the left while pulling upward — the lift-and-turn type especially should release with this motion. If the plug refuses to move or isn't sealing properly, replacing it is generally the more straightforward solution.

Cross-section diagram of toilet labelling cistern, flush valve, internal trap and waste pipe

Tackling Smelly Toilet Drains

While a smelly bath drain is usually resolved once the plug issue is sorted, smells coming from your toilet may require something more.

If your toilet is the culprit, the drain itself may not be the issue. The problem may be an improperly installed wax ring at the base of the toilet bowl, a cracked toilet pan, or worn toilet parts — such as the fill valve or flush valve — releasing waste gas into your home through the cistern. A fill valve that isn't keeping the cistern full can leave the internal trap exposed, which is a surprisingly common cause of toilet odour.

The key is diagnosis. Is there an odour near the base of the toilet? Check the wax ring first. Is the smell coming from inside the bowl or cistern? Then inspect the fill valve and flush valve. Replacing a fill valve is a DIY task, but anything involving your toilet's waste pipes, traps, or pan connection must be handled by a licensed plumber, as required by Australian state and territory plumbing licensing legislation. If you notice gurgling sounds, persistent odour after cleaning, or slow drainage across multiple fixtures, call a licensed plumber promptly.

References

AS/NZS 3500.2:2025 Plumbing and Drainage — Sanitary Plumbing and Drainage, Standards Australia

National Construction Code 2025, ABCB Housing Provisions, Part 10.8 Condensation management

WaterMark Certification Scheme, Australian Building Codes Board

State and territory plumbing licensing authorities (Building and Plumbing Commission Victoria; Building Commission NSW / NSW Fair Trading; Queensland Building and Construction Commission; Plumbers Licensing Board Western Australia (administered by Building and Energy); Consumer, Building and Occupational Services Tasmania; Access Canberra ACT; Office of the Technical Regulator / Consumer and Business Services South Australia; Plumbers and Drainers Licensing Board Northern Territory)

FAQs

How often should you replace an enzyme-based drain cleaner versus using the bicarb-and-vinegar method?

Enzyme-based cleaners work more slowly than the fizzing bicarb method — typically needing an overnight dwell time — but they're genuinely better at breaking down grease in kitchen sink pipes over the long term. A practical approach is to use the bicarb-and-vinegar flush monthly for maintenance, and reach for an enzyme cleaner every three to four months for a deeper treatment.

Can a smelly drain be a sign that your P-trap is incorrectly sized or installed, rather than just dried out?

Absolutely — an undersized or poorly fitted P-trap won't hold an adequate water seal even with regular use, meaning sewer gas escapes continuously rather than only when the fixture sits idle. If flushing the drain with water doesn't resolve the smell within a day or two, it's worth having a licensed plumber inspect the trap configuration itself.

Is it safe to use bicarb and vinegar in drains connected to a septic system?

Yes, in the quantities described here it's fine — the reaction neutralises before reaching the tank and won't disrupt the bacterial activity your septic system depends on. Avoid harsh chemical drain cleaners if you're on septic, as those can genuinely damage the microbial balance.