How to Unblock a Sink Using Sodium Hydroxide

by Lucy Bell-Young

Sodium hydroxide (NaOH) is a strongly alkaline compound that appears as a white solid. It is commonly used in the manufacture of soap and detergents, but did you know that it can also help unblock your sink?

Use Sodium Hydroxide to Unblock Your Sink

As a strong base that is very reactive, there are several ways that sodium hydroxide can unblock household sinks, drains and pipes. When handling this substance, it is important to wear the appropriate protective clothing since it is very corrosive to skin contact.

Using such a caustic chemical on household appliances may sound dangerous, but sodium hydroxide is actually the active ingredient in nearly every serious drain cleaner – so you have probably used it before without even realising.

How to Make Your Own Sink Cleaner

While sodium hydroxide is used in commercial drain unblockers, you can actually make your own bottle of the good stuff at home:

  • Fill a container, like a bottle or a bucket, most of the way with cold water. You can use a glass or plastic container, but avoid using any metal since it will react with the sodium hydroxide
  • Add 3 cups of sodium hydroxide to the water and stir with a plastic or wooden spoon. The mixture will begin to fizz and heat up in an exothermic reaction with the water
  • Pour your aqueous solution of sodium hydroxide into your sink or drain and wait for 30 minutes before rinsing with boiling water

After washing away the sodium hydroxide solution, your sink should be unblocked and as good as new. The mechanism of how NaOH achieves this goes far beyond the simple fact that it is corrosive. When used to unblock drains, pipes or sinks, sodium hydroxide actually undergoes many reactions.

A rustic sink in a kitchen

How Does it Work?

There are three main reactions that happen when sodium hydroxide is used as an unblocker. These are also some of the most characteristic reactions of NaOH and give insight into its properties.

  1. Saponification

One of the most famous reactions involving sodium hydroxide is saponification, a process that produces soap. This is why NaOH is widely used in the manufacture of soaps and shampoos.

Chemically, saponification happens because of the reaction between triglycerides and sodium hydroxide. Triglycerides are the main components of animal fats or vegetal oils and are esters that are derived from glycerol and three fatty acid groups.

When triglycerides react with sodium hydroxide, they get converted into glycerol and a fatty acid salt, i.e. ‘soap.’ This is why when NaOH comes into contact with skin, it feels slippery because of how it is reacting with and changing the natural oils in your skin – though it is important to always avoid skin contact!

Therefore, saponification is the alkaline hydrolysis of fatty acid esters. This process is used in wet chemical fire extinguishers because it can change the burning oils or fats into non-combustible soap. Saponification is also one of the ways sodium hydroxide can unblock your sink.

When a sink or drain is blocked, it is usually because of a build-up of fats and grease. The presence of sodium hydroxide, either as an ingredient in a cleaner or as a home-made aqueous solution, kick-starts saponification and converts these pesky fats into soaps. The soap is then easily dissolved and removed by water.

  1. Exothermic Reaction

Because it is extremely basic, when sodium hydroxide dissolves in water it completely disassociates into Na+ and OH- ions. Not only will this produce a caustic solution with a high pH, it will also release a lot of heat.

Sodium hydroxide has an exothermic reaction with water because of the presence of OH- ions, which are very stable. The heat being emitted is also a result of the energy state of the chemical species being lowered. In fact, the intensity of this reaction is what makes NaOH crystals well-suited as powerful desiccants in many industrial processes.

This exothermic reaction with water is very useful in sinks and drains because an aqueous solution of sodium hydroxide will be able to melt away the blockage quite easily.

When used in this way, it is crucial to follow safety precautions for 2 reasons: sodium hydroxide is extremely caustic and can cause severe burns, and the heat produced in this reaction could cause the solution to boil and splash back, which could cause burns and even blindness if it reaches your eyes.

  1. Aluminium

Sodium hydroxide’s reaction with aluminium metal also plays a role in its ability to unblock your sink. This is because many sinks and drains contain small pieces of aluminium.

When these two compounds react, one of the by-products is hydrogen gas. In large quantities, this rapid evolution of hydrogen gas can be used to fill airships, hot air balloons and has even been proposed as a source of fuel for hydrogen-powered cars.

In small quantities, like in sinks, the tiny bubbles of hydrogen gas being produced can actually help to dislodge the blockage by agitating the NaOH solution.

Someone cupping their hands holding soap bubbles under a tap

Sodium hydroxide is a versatile chemical that has a wide range of uses beyond its ability to unblock your sink. ReAgent has a huge variety of NaOH products for sale online. Place your order today or contact a member of the team to discuss any technical queries you may have.


The blog on and everything published on it is provided as an information resource only. The blog, its authors and affiliates accept no responsibility for any accident, injury or damage caused in part or directly from following the information provided on this website. We do not recommend using any chemical without first consulting the Material Safety Data Sheet which can be obtained from the manufacturer and following the safety advice and precautions on the product label. If you are in any doubt about health and safety issues please consult the Health & Safety Executive (HSE).