Why Does The Kitchen Sink Gurgle When The Toilet Is Flushed?

Why Does The Kitchen Sink Gurgle When The Toilet Is Flushed?

Anthony Barnes

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There is nothing more annoying than the deafening sound of your sink gurgling.

It can often be a sign of damaged pipes or a clog of debris in the plumbing system somewhere!

So it is important to check that everything is working smoothly, so that there are no nasty surprises in your kitchen or bathroom. 

With this handy article, you’ll be able to do these important checks yourself and learn how to adjust and fix your plumbing system, without needing help from a professional plumber.

Not only will this save you time and money, but knowing how your plumbing and ventilation system works is a must for any homeowner! 

So, let’s get to the root of the problem by following the simple steps below and answer the question; why does the sink gurgle when the toilet is flushed?

How Your Plumbing System Works

These days, every modern plumbing system is practically identical, consisting of various drain pipes and vents.

Modern plumbing systems have 3 main purposes, which are;

  • To Drain Waste – Many pipes are used to move debris and water down into the main skewers.
  • Creating A Water Seal – A water seal prevents any nasty sewer gases from entering and flowing around your home.
  • To Vent Air – Vents keep the water flowing freely and protect the water seal by using ventilation.

Using a sink vent is an important part of any plumbing system as it is vital for draining and forming the water seal.

A vent stack is the configuration of your pipes. A long pipe runs all the way from the sewer to the roof in traditional plumbing systems and this is known as a wet vent.

By using a wet vent, fixtures like the toilet and sinks in your home share a pipe that drains all the water downward into the sweater pipe and pulls air through the outside roof vent at the exact same time. This is also known as external venting.

Why Does The Kitchen Sink Gurgle When The Toilet Is Flushed?

By Installing a vent directly under your sink, another way of ventilating a plumbing system is created.

This removes the need for a wet vent. An air admittance valve, also known as a cheater valve can be installed on the trap. 

Each Fixture has its own trap, creating a water seal and preventing any sewer gases from rising up into your home.

Often, the gurgling noises that can be heard are happening in the plumbing trap itself, located under the sink. This particular trap is known as the P trap or S trap.

S traps are generally no longer used in newer structures. But are present in older homes or properties.

If you have an older S trap in your home, it should be replaced with a newer and more efficient P trap or retrofitted with an air admittance valve instead.

Otherwise, you will find that the problem with the water seal continues.

How To Quiet Your Gurgling Kitchen Sink

The vacuum system in the pipes will pull air from another plumbing fixture if there is no access to outside air.

So essentially, by flushing your toilet, air is pulled from the sink, removing the water from the trap.

This is likely to be the cause if your sink makes a gurgling sound but still drains fine. In order to correct this problem, you will need;

  • To make sure that any vents that have been installed are working correctly. 
  • Inspect all of the pipes to ensure they are not clogged.

If one of the vents is blocked by debris, the trap seal can be sucked out with the draining water, causing the gurgling sound.

The buildup of debris inside the trap can also cause the seal to drain.

Why Does The Kitchen Sink Gurgle When The Toilet Is Flushed?

As well as debris, any hair and fabric caught inside the trap can cause the water to leak out, removing the water seal.

By following the steps below, you can stop your sink from gurgling and keep your pipes in working order!

Checking The Main Vent Pipe

 Alongside the kitchen pipes gurgling, the toilet may also flush on its own occasionally, if you have a clogged main vent stack.

To correct this, use a ladder to carefully get up on the roof and with a flashlight, check down the main pipe for any blockages.

If you can see a build up, you will need to reach it and clear it out. If the blockage is too far down to reach, you might need to hire a snake or auger to do so.

When the weather is colder, the pipes may often freeze over and will need to be cleared.

Climbing up to your roof when it is icy is not the safest course of action, and in those conditions it is recommended that you call a professional. 

Checking For Blockages Inside The Drainage Pipe

If the drainage pipe doesn’t receive enough flow, the water will drain too slowly.

If you notice a slow moving drain, then it is likely you will need to clear out the trap.

In order to do this, you will need to remove the trap and remove any debris inside. 

  • Put a bucket or cloth directly underneath the trap and use pliers to remove the coupling, which attaches the trap to the sink. 
  • Using a wired brush or a metal hanger, clean out the trap thoroughly. 
  • Once you’ve rinsed the trap out, put everything back together and see if the drain is now working correctly. This should solve the problem.
Why Does The Kitchen Sink Gurgle When The Toilet Is Flushed?

Checking The Air Admittance Valve

Usually an air admittance valve will remain in working order for at least 20 years, without any issues but over a long period of time, they can start to fail.

If you can see that you have an air admittance valve installed onto your trap, you should also check it to ensure it’s still in correct working order.

The gurgling sound that you can hear could be because the valve is stuck in the closed position.

The noise could also be from clogging, improper fitting or damage to the valve.

  • Try to remove the valve and then run the sink to see if that helps.
  • If the water starts to drain properly, it probably means that the vent is not working as it should. Try not to run the water for too long without the valve attached or you may flood the pipes and cause quite a mess.
  • Make sure to inspect the valve for any damage or debris clogged inside. If you do find debris, clean it out and reattach it to the sink to see if it now drains properly.

Final Thoughts

By checking all of these features in your plumbing system, you should be able to find the source of what is causing the gurgling noise and finally be able to solve both the problem and answer your question!

If you struggle with any of the steps below or feel that the cause of the gurgling is damage to any of the pipes, valves or other parts, then it might be worth contacting a professional, rather than trying to rectify it yourself and cause more damage.

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By Anthony Barnes

Anthony Barnes is the founder of Water Heater Hub and a second-generation plumber by profession. Before developing Water Heater Hub, Anthony Barnes was a full-time plumber, and he has undertaken a wide variety of projects over the decades. As a second-generation plumber, it was easy for Anthony to get used to the technicalities of all from a tender age