If your drain is working well, and there isn’t a build-up of material somewhere along the plumbing system, then your drains won’t really smell. So if you’ve noticed smelly drains in the house or smelly drains outside, that’s an indication that something is wrong, and the sooner you can fix the problem, the better. There are various reasons why a drain might have a bad odour. Some of the causes you will be able to remedy by yourself, but others will be more complex and will require the help of an expert.

In this article, we will discuss the various methods you can use to remedy the problem – or at least neutralise some of the odour until the experts arrive. We will go over some of the reasons drains smell, how to figure out what kind of build-up you have, and how to treat it.

What Causes Smelly Drains?

A bad smell usually indicates an accumulation of bacteria. Bacteria accumulates on any blockages or build-up of organic materials within the plumbing of your house. This can happen when food, hair, grease, soaps, minerals, or objects are washed into the drains, causing blockages somewhere along the drain pipes. Luckily you can typically clean these blockages out by yourself using home remedies.

However, smells can also indicate plumbing issues, such as a dried out, or leaking U-bend under the sink, or eroding/cracked pipes, if you have old plumbing. In some cases, it could even be a problem with the main sewers.

How to Identify the Problem?

The first step to treating your smelly drains is to identify the problem. First of all, where is the drain located? Blockages that occur in your kitchen sink will be made from different materials than those in your bathroom, or in an outside drain.

A blockage in your kitchen is likely caused, primarily, by grease and food scraps. Whereas your bathroom drains could be blocked by residues leftover from personal hygiene products like shampoo, or unflushable items, such as wet wipes. Outdoor drains are more likely to be blocked by leaves and trash.

Other than location, you can also use smell to try to identify the problem. Different problems will result in different odours coming from your drain.

A typical drain blockage found in either a kitchen or bathroom will usually result in a smell that can be similar to bad breath, or damp clothes. You will also notice that water drains more slowly than expected, however, this sign can come quite some time after you first notice the bad smell.

If your drain smells metallic or like decay, you might have eroding pipes in your plumbing. Over time old pipework can rust or become calcified, which will eventually result in smelly drains.

If you can smell sewage from a drain inside your home, that could indicate a blocked toilet, or an empty P-trap, for example.

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How to Get Rid of Smelly Drains

How to clean smelly drains depends on the reason for the smell. We can break it down into drains inside the home and drains outside the home.

Fix Smelly Drains in the House

If you suspect that you have a blockage in the drains of your home, you will have to tailor the treatment you use for the type of blockage.

Fix Smelly Kitchen Drains

In the kitchen, you are most likely to have a blockage made up of leftover food, grease, and small pieces of broken glass or ceramics. The blockage could be under the sink, or inside/behind your dishwasher.

If the smell is coming from the kitchen sink, then follow these steps:

  1. Clear the Area

Clear away any visible waste, in order to stop it from entering the drain and adding to the clog.

  1. Boiling Water

Pour boiling water with a little dishwashing detergent down the drain. The boiling water will start to break up the fats, and soften any food matter. The detergent aids this process. You should repeat this several times.

  1. Baking Soda

Baking soda is great for neutralising smells, especially musty smells. Baking soda is good at breaking down mineral build-up in pipes too, so can help loosen up chunks of residue.

To use, pour some baking soda down the drain and leave for an hour or two. Slowly and steadily pour a few litres of boiling water down the drain. The reaction between the water & baking soda will help break up some fats, the high temperature of the water helps too.

  1. Check if the drain is too dry

A dry drain can mean sewage smells. Your drainage system uses the push and pull of water and air to help liquid flow through your pipes. The water in your pipe also prevents gases from the sewers from escaping the drains into your home. So if you’ve noticed a sewage-like smell coming from your drains, then you may have just not been using it enough. This can also happen if you’ve been away for a while, for example. The problem should be easily resolved by running the taps frequently, to prevent them from drying out too much inside.

  1. Check your dishwasher

Dishwasher drains are usually connected to the kitchen sink drain. If this is the case, a smelly drain could be the result of a blockage somewhere in your dishwasher or dishwasher drain pipe. You can usually tell if you have a blocked dishwasher, as you might find there is a fishy or rotten smell coming from it. You might also have noticed that your dishes are coming out less clean than usual.

Click here to read our step-by-step article on how to clean a blocked dishwasher if you suspect this is your problem.

  1. Consider getting a professional

If the above methods haven’t helped, then it is likely that the problem is more complex than at first glance. You might be able to fix some of these problems by yourself if you are feeling adventurous, such as a blocked U-bend, or P-trap. However, others, like a blocked drainage vent, or eroding & cracked pipes, will need a professionals’ knowledge and tools to repair.

  1. Unblocking a U-bend

If you think you have a stubborn blockage a bit deeper down the pipes in your sink, you could try using a drain-snake (drain cleaning rod) to clear it out. Failing that, you could remove the u-bend, using a wrench to unscrew it, and clean it out with a wire brush. However, if you’re not confident, it is best to hire a plumber.

Fix Smelly Bathroom Drains

Blockages in bathroom drains will be different to those in the kitchen, so although most of the way we treat them will be the same, there are some differences. In the bathroom, blockages tend to be made up of hair, soap and lotion residues, mineral build-ups, and “unflushables”, which are non-compostable items, such as wet wipes, sanitary products, or floss.

These types of drains can accumulate debris very quickly because they gather hair. Typically, hair will enter the drain and get stuck, which will inevitably catch other debris as it is carried down via the water.

  1. Remove the hair

The first step will be to try and remove the hair, you can use a drain-snake (drain cleaning rod) to assist you, otherwise, a toothbrush or a long piece of wire might do it. Once you’ve removed as much hair as possible, you will want to break up the soaps and lotions which may have built up around the hair.

As well as following the steps outlined above in the kitchen drain section, there are a few additional steps:

  1. Vinegar

Vinegar is an acid, which has many applications in cleaning. Acids are great for breaking down soap scum and mineral deposits. To make the most of the vinegar, bring some to a simmer and pour it, slowly and steadily, down the drain. Leave it for an hour or two and rinse with boiling water.

  1. Check for a blocked toilet

Your toilet might be blocked, which is causing the drainage system to function poorly. This can happen through a build-up of minerals and organic matter, as well as through the improper disposable of “unflushables”. If you have a blocked toilet, you will likely also find that you have problems flushing. If this is the case then you can use a plunger to try to unclog the toilet pipe, but if this doesn’t work then you will have to hire a plumber.

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Fix a Smelly Washing Machine

Washing machine drains can become clogged up with thick washing detergents, which can build up at a rapid pace. This build-up gives a surface for bacteria to adhere to, which will cause a smell. The best fix for this is to run a cycle on your washing machine with a cup of vinegar to help break down the detergent. If this doesn’t help, then you will likely need to call in a professional to identify the problem, as washing machines and drainage systems are quite complex.


Fix Smelly Drains Outside

Drains outside are usually more likely to have a bad smell than indoor drains, as they exist in a changeable environment, with a lot of organic debris and trash. Unfortunately, outside drains typically have more complicated issues associate with them.

You can apply the same techniques described above for indoor drains, to outdoor drains. However, outdoor drains could stem from a problem with your houses plumbing, or a bigger problem with the street or areas plumbing. For this reason, it is always best to call a professional for outdoor drains, so they can identify where the problem lies.

If the problem isn’t within the plumbing system of your home, then the cause of the problem is going to be much more difficult to find. If the pipe is blocked far down the line, then it will require specialist equipment and expert knowledge to unblock it. If you aren’t able to solve the problem by yourself, then it is time to call in help. You can contact a drainage contractor to carry out an inspection of your drains. A CCTV survey will identify any blockages or damage, allowing it to be repaired.

You might even find that the problem is to do with the main sewers, which could be caused by a fatberg, drain collapse, or corrosion, so even if the problem isn’t on your property, it is important to report smelly drains to your local authority.

Fix a Smelly Septic tank

If you have a septic tank, and you can smell sewage sometimes when you are outside, then your tank could be the cause. There are a few reasons why your septic tank might smell.

Your tank could be full. When septic tanks start to reach capacity, they can start to smell. There are two solutions to this. You can get your tank emptied, or you could add a bacteria top-up treatment which will add beneficial bacteria to your septic system, to break down the organic matter more quickly, thereby reducing odours.

The seal could be broken, or your tank could be cracked. Over time, the tanks can become compromised from repeated freezing temperatures and general decay from sitting in the ground for years and holding waste. When the lid, or seal, of your tank starts to deteriorate, you will begin to notice a smell coming from the area near where your tank is buried. In this case, you will have to get in touch with your supplier, or installer, to ask for advice.

Important Warnings & General Advice

Do not mix bleach with other chemicals, such as acids like vinegar or other cleaning supplies, as this will cause it to emit chlorine gas which is highly toxic.  If inhaled, it can cause breathing problems, burning eyes, vomiting, pneumonia, and even death.  Be very careful to thoroughly rinse your drains with water after treating them with any chemicals – leave the taps on for several minutes. This will not only protect your health, but also your plumbing, as chemical reactions between products within the pipes can cause damage, which can lead to cracked or burst pipes.

Be aware that using powerful store-bought drain cleaners can have adverse effects on your plumbing, as they are highly corrosive. If your smelly drain is caused by corroded pipes, then a corrosive chemical could make the problem worse. If in doubt, consult a professional. If you do choose to use a drain cleaner, then be sure to read the directions on the label thoroughly and adhere to them.

You should never use strong chemicals such as drain cleaner, or bleach, if you have a septic tank, as this will destroy the beneficial bacteria which live in the septic system. These bacteria break down the waste and prevent smells.

Although not dangerous, ensure that you use the vinegar and the baking soda separately when cleaning your drains. Vinegar is an acid, baking soda is alkaline, so they effectively neutralise each other when combined. This means that when you mix them, the chemical reaction causes them to fit up, but then you are left with water, carbon dioxide and sodium acetate (slightly alkaline salt). This reaction is great for removing stains in fabrics, or surface grime. But in a drain, it often can’t distribute quickly enough before the reaction is over. So, in order to get the most benefit from them both, we advise you to use them separately when cleaning drains.


In this article, we have discussed some of the reasons why drains smell, how to figure out what kind of build-up you have, and how to treat it. The cause behind a smelly drain could be superficial or complex, so trying the simple steps could save you some time and money in the long run, however, if nothing here has helped you, then you will have to hire a professional to fix the underlying issue.

In some cases, the issue might not be on your property, and so won’t be your responsibility. For example, abnormalities in the main sewer line. This is why even if it isn’t on your property, it is important to report the issue to the local authorities.

Consider adding cleaning your drains onto your list of regular chores. Pouring boiling water down your drains, or even running a tap on an unused sink every few days will help your drains stay clean and clear.


Skills Training Group is an award-winning provider of gas apprenticeship, plumbing, electrical & first aid courses. For further information on our range courses, contact a member of our team on 0141 889 4516.

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