Causes of a Smelly Sink Drain & How to Fix It

One of the most unpleasant and frustrating problems to have in your home or place of work is a smelly sink drain. Fortunately, while there are many reasons your bathroom or kitchen sink might have started smelling, there are also multiple ways to fix it – including using home remedies that might not cost you anything at all.

Causes of a Smelly Sink

There is not one single cause of a smelly sink drain. Instead, there are a number of reasons why there might be foul-smelling odours coming from your kitchen or bathroom. We’ve listed the most common reasons below, as these are more likely to be the reason there is a smell coming from your drains in the first place:

Food Debris

When plates with food on are not scraped off properly before being washed in the kitchen sink, the pieces, scraps, and particles left over can collect together in the pipes underneath. This waste gets captured by the biofilm in your U-bend, compacts, and results in a blocked sink. As the debris then starts rotting it will allow bacteria to thrive and create a smell.


Fats, oils, and grease (sometimes known collectively as “FOG”) is a very similar cause to the problem of food debris. When any of these are poured into your drains instead of removed and put in a household waste bin, they cling to the pipes and will eventually solidify. This also blocks the drains and can produce a smell.

In a kitchen sink, the FOG will come from food. But it is also possible to experience a FOG blockage in a bathroom sink – through soap scum and particles, toothpaste, and shaving foam that gets washed into the drains.


When washing, it is likely that you will also shed some hair. This also has the potential to cause a blockage in your drains because it accumulates and mixes with soap scum, shampoo, shower gel, toothpaste, and shaving foam to form one congealed mass. 

Plumbing Issues

It may be the case that your drain smells because the plumbing system itself isn’t in its best condition. If there is a missing grease trap or vent, a leak, or even a rusted or rotting drain tube then you might experience a bad smell in the room.

Sewer Gases

You may be smelling sewer gases coming from your drains, which might indicate that your sink has an empty P-trap.

How to Get Rid of Sink Drain Smells

As with causes of smelly sink drains, there are also a range of different methods you can use to get rid of the smell. The best method for you to use is likely to depend on the sink that is currently affected, however. We have divided our advice up into methods for bathroom and kitchen sinks below, so you can follow the set of instructions which suits your needs most.

Before You Begin

Before you start trying to clean or clear out a smelly sink drain, there are some points you should bear in mind:

  • Always ensure you have some safety gear on hand – particularly rubber gloves and safety goggles to prevent splashes
  • Start the work by clearing the drain opening of waste – food if you’re working on a kitchen sink, hair and soap scum if you are working on a bathroom sink
  • Pouring boiling hot water down the drain, waiting five minutes, and flushing this with cold water should help to wash away buildups of grease

How to Fix a Smelly Kitchen Sink Drain

Cleaner in rubber gloves shows clean plughole protector of a kitchen sink

Here we have provided instructions on how to get rid of smells in a kitchen sink drain:

Diagnose the cause of the smell

The first thing you will need to do is work out what is causing the smell in the first place. If you notice that water is draining slowly or not at all, this will mean that there is something clogging the pipes – causing a blockage and most likely the smell as well. 

If the smell is one of rotting food, then rotting food blocking the pipe is probably the cause. It may also be grease, fats, and oils sticking to the sides of the pipe. If the smell is of rotten egg, this means that sewer gases are probably escaping up the pipe through the U-bend.

How to stop the smell

There are a range of home remedies to get rid of the smell in a kitchen sink drain. Some can be carried out using items you probably already have in your home, while others may require going to the shops and buying extra items.

  1. The boiling water method:
    1. Boil a pan or kettle of water
    2. Slowly pour the water down the plughole
    3. Wait five minutes
    4. Run the cold tap to force the remaining grease to congeal and flush through
  2. The white vinegar method:
    1. Pour a small amount of white vinegar down the plughole
    2. Let the vinegar stand for half an hour (30 minutes)
    3. Flush the drain through with hot water
  3. The baking soda and vinegar method:
    1. Carefully pour half a cup of baking soda down the plughole
    2. Pour one cup of vinegar down the plughole after the baking soda
    3. Let the solution foam up; leave it for an hour or more to work
    4. Pour hot boiling water down the sink after an hour to flush it through
  4. The drain cleaner method
    1. Buy a chemical cleaner that is designed for sink drains
    2. Follow the instructions on the label as you use the cleaner

Checking the P-trap or U-bend

The U-bend under the kitchen sink is also a sewer gas trap that you might hear referred to as the “P-trap”. Because it is designed to trap gas, it should always be full of water – to act as a barrier and stop sewer gases from escaping out of the plughole.

You can help to stop sewer gas smells from making their way into your kitchen by:

  1. Checking if the water in your U-bend has evaporated, which can happen if you have been away and not run the water for some time. Running the water should fix it.
  2. Checking if there is a leak in the U-bend; this can be done by checking for drips or damp patches under the sink. If there is a leak, a professional plumber or drainage expert should then be called.
  1. Checking if there is a blockage in the U-bend; try cleaning out the sink drain, but if there is still a blockage after this you may need to remove the U-bend and clean it out with a wire brush.

How to Fix a Smelly Bathroom Sink Drain

The methods we have mentioned above can all be used to help stop smells coming from bathroom sink drains. But there are also some other points and instructions which may apply to bathroom sinks in particular:

Check the overflow pipe

The small hole close to the top of a sink basin is what is known as the overflow. It is there to prevent the sink from overflowing, by allowing water to drain away if the level in a sink gets too high. This overflow hole also has a tendency to catch soap scum and other types of buildup. As a result, it may start to smell over time.

Like a plughole, you can clean out the overflow by using the white vinegar method, or by pouring a suitable amount of bleach down the hole. You may also consider buying an extra toothbrush, or another kind of brush small enough to fit inside, to scrub out the inside of the overflow’s rim on a regular basis.

Clean the sink basin

It might be the case that the cause of your stinky sink is not in the drains. There might be buildup in the basin itself as well. This is usually more common in kitchen sinks, where food particles will build up over time, but this does not mean that it cannot happen elsewhere in your home. 

Simply clean the sink by closing the drain, adding some soap and hot or boiling water, and leaving it for a few minutes. As you let the water drain away, you should scrub at the sides of the basin. This might help to eliminate the cause of the smell, if it is the basin that’s the problem.

Preventing Sink Drain Smell

It is easy to prevent a smelly sink drain, using any of the methods we have provided here:

  • Placing a drain screen or sink strainer over the plughole; this will catch food particles in kitchen sinks and hair and soap scum in bathroom sinks
  • Avoid pouring fats, oils, and grease down kitchen drains; instead, use kitchen towel to absorb as much of it as possible and throw it away in a bin before washing up
  • Every time you boil a kettle, pour the leftover hot water down the drain to kill off bacteria
  • Pour baking soda down your drains at least once a week; this is especially important if you are going away and will not be using your sinks for a while
  • Schedule regular checks, maintenance, and care with a professional plumbing and drainage service 

When to Call a Professional

If all of the methods we have listed above do not help your smelly sink drain, it will be time for you to call a professional service to find out the cause. An experienced plumbing and drainage company will have a range of tools designed for carrying out thorough investigations, such as those completed during CCTV drain surveys. They should also have the skills and knowledge necessary to quickly come up with a solution to get the problem taken care of.

Need Help with Smelly Drains?

Our Emergency Plumbing Services

If there is a problem causing your drains to smell and you cannot tell what it is, or even if you know what the problem is but not how to fix it, contact BlockBusters today. Our team will be ready and waiting to send one of our experts out to your property, so they can find the cause of your drain smell, come up with a solution, and get it fixed as soon as possible.

With no call-out charges, no fees on repair quotes, and competitive prices on all of our services, you are also guaranteed to save money from your household budget. Get in touch with us whenever you are having problems with a drain smell that just won’t go away and let us help you to clear the air.

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