5 reasons why your sink won’t drain – and how to fix it

When your sink is slow running or blocked, it’s not draining properly. Here are five reasons why your sink won't drain and how to fix it

sink with water draining
(Image credit: Alamy)

One of the most irritating things when it comes to plumbing is when the sink won’t drain. Whether it’s the kitchen or utility sink or the basin in the bathroom or en-suite, it’s something that needs to be sorted asap as it rarely remedies itself.

The approach you take when unclogging a sink that won't drain really depends on the cause of the blockage.

‘There are a variety of reasons why a sink could be slow-running or blocked,’ says Kevin Began, director at Blockbusters Drainage and Plumbing Services (opens in new tab). ‘One common problem is food debris caught in the U-bend or trap under the sink. This can be difficult to remedy yourself, so it’s best to contact a professional who will carefully remove the bend or trap while catching any wastewater within a receptacle to prevent overflows or leaks. Another common cause can be sediment within the small-bore pipework, which can build up over time.’

Here are the five most common reasons why a sink won't drain.

Why a sink won't drain, and what to do

Often a sink won't drain because you have been allowing food or cooking ingredients into the drain itself. These are the main causes, and their remedies.

1. Solidification of grease and fats

Plumbing expert David Cruz of My Job Quote (opens in new tab) explains that fats solidify quickly, causing a tough blockage in your drain. ‘If you’ve ever seen how fat hardens on Saran Wrap or drained fat from a roast chicken into a container, you'll know that it hardens into a complex, white block of solid fat after a short time,’ he says. ‘So never pour fat down the sink. Instead, drain it into a cup to harden before disposing of it.’

2. Chemicals and soap

‘Soap, cleaning fluids or chemicals can all cause drain blockages. First, consider whether it makes sense that cleaners could cause such a problem. This occurs when mineral deposits combine with soap or chemical products, resulting in scum that becomes thick enough to clog sink drains.’

3. Hair accumulation 

Just like when unclogging a shower drain or unclogging a bathtub drain, hair can be a culprit in a sink.

‘Loose hairs unknowingly rinsed down the drain tend to clog bathroom sinks. The longer they are, the more chaos they can cause and when clumps of hair accumulate over time, you have a recipe for a blocked drain disaster.’

4. Debris and dirt 

‘This issue can occur in a kitchen or even a bathroom drain. Cleaning up after indoor plant potting for instance, could result in a build of dirt and debris, resulting in drainage issues.’

5. Blocked external drains

‘Kitchen sinks can also be affected as a result of external drains being blocked,’ adds Kevin Began, director at Blockbusters Drainage and Plumbing Services. ‘For example, if the inspection chamber is full, this can lead to a kitchen sink refusing to clear. In these instances, a drain engineer would inspect all the relevant facilities before conducting the clearance of the external inspection chambers with high-pressure water jetting. 

‘The facilities would be checked again and, if a drainage engineer discovers an underlying fault that may have caused the blockage, a CCTV drain survey would be required to view any potential problems within the pipework itself. The footage from this survey would be used to produce a report identifying any issues found – providing recommendations for remedial repair and a costing.’

6 fixes to try if your sink won't drain

There are some easy remedies that you can try before calling the experts in…

1. Use a plunger

It’s always handy to have a plunger around the house. You can buy one from a DIY store and simply cover the plughole with the plunger, making sure it seals in place. Pump for a few minutes. The plunger sucks air in and out of the drain, which will help to dislodge any build-up of food debris.

2. Pour hot water from a kettle

Boiling water can help clear a blocked sink so pop the kettle on and pour down the drain. Leave for a while then try again. The heat of the water can sometimes force things through.

3. Try baking soda and vinegar

Cleaning with baking soda and cleaning with vinegar can be really effective. If your sink won't drain, mix half a cup of baking soda with the same amount of salt and pour down the sink drain. Leave for a few hours then rinse with boiling water. Alternatively, pour a cup full of baking soda into the drain then follow with the same amount of white or apple cider vinegar. It should start to foam immediately so pop the drain stopper in and leave for 10 minutes. Flush with boiling water.

4. Buy a drain cleaning product

If none of the above work, you might want to buy a specialist drain unblocking solution. Some are more eco-friendly than others so check the label and choose one that won’t harm wildlife, plants and waterways.

5. Check the P-trap

Look under the sink at the pipework. The U-shape can sometimes hold a build-up of food or debris so pop a bucket underneath and unscrew this section to see if anything is blocking it. Screw back on tightly and check if that’s done the job.

6. Use a plumber's snake

This specialist piece of equipment is a long wire that is placed down the drain with a handle at one end. Turn the handle for a screwcork effect that can help remove debris, enabling you to pull it out. You can buy plumbing snakes at Amazon; this is our favorite buy (opens in new tab).

Can I use Drano if my sink won't drain?

Drano is suitable for unclogging a sink that won't drain. Simply empty the sink of water into a bowl or bucket, pour in the product, leave for 15 to 30 minutes then flush with boiling water. Repeat if necessary but do not use Drano on unless your sink is clogged. You can buy Drano at Amazon (opens in new tab).

Will bleach make my sink drain?

Bleach will not make your sink drain. Bleach should be used to sanitize and deodorize drains, but it will not cure a sink that won't drain because it cannot dissolve food debris and hair.

How can I prevent my sink not draining in future?

Use a sink drain stopper with small holes in it, as this will catch most bits of food and debris that can otherwise go down the drain. Think about the soap you’re using and never pour fats down the sink.

How can I force a sink to drain?

Pour some boiling water down the sink and the heat of it should help to break up any clogs. Otherwise try the baking soda and white vinegar solution, which will foam and bubble to help dislodge any debris.

Hayley Gilbert
Hayley Gilbert

Hayley is an interiors journalist, content provider and copywriter with 26 years experience who has contributed to a wide range of consumer magazines, trade titles, newspapers, blogs and online content. Specialising in kitchens and bathrooms, she has twice won the CEDIA Award for Best Technology feature. Hayley writes for H&G about kitchens, bathrooms, cleaning, DIY and organizing.