Why Sink Gurgles When Toilet Flushes? (Explained)

The plumbing system in the household is anything but silent, and we are all used to that. However, when you hear gurgling in the sink, there is definitely some problem; most often, it is a blockage in the system. In this article, we’ll explain why a bathroom sink gurgles during toilet flush. So, let’s start!

Why Sink Gurgles When Toilet Flushes? Usually, the sink gurgles during the toilet flush when something obstructs the normal flow of water in the main pipe vent. In most cases, it’s the blockage and can be recognized by the appearance of bubbles in the drain. By removing the blockage, the sink gurgles will stop during the toilet flush.

Although this problem is not uncommon, it is recommended that you hire a professional for this job. Not every gurgling sound from a pipe means the same problem. For example, if you notice gurgling and bubbles without flushing the toilet, the cause can be air in the P-trap. In the next chapter, we’ll explain the main reasons why this problem occurs.

What Causes A Gurgling Sink When Your Toilet Is Flushed?

Gurgling Sink When Toilet Is Flushed

In most cases, when you hear gurgling in the sink after you flush the toilet, it is a sign that there is a clog in the pipes, due to which the balance in the circulation of water and air through the home plumbing system has been disturbed.

1. There Is A Blocked Drain

A gurgling sound from the sink most often means that you are facing a problem related to a clogged drain system. In the average American household, it is usually caused by accumulations of things such as: dead skin, hair, dirt, oils, soap, and used wipes. Depending on your water flow from the sink to the drain, you can conclude whether your drain is blocked completely or only partially.

  • Completely blocked – You can tell that the drain in your house is completely blocked when water accumulates in it without going to the drain at all. This usually happens after a slow, draining problem for a few days.
  • Partially blocked – Regardless of the volume of the gurgling sound, if the water from your sink still flows into the drain but slower than usual, the drain is only partially blocked. You must act immediately if you want to prevent the drain from becoming completely blocked.

To understand this topic better, we recommend you to read: Parts of a Toilet and How It Works (Plumbing Diagrams).

2. There Is A Blocked Sewer Line

The sewer line is a set of drainage pipes that drains wastewater from your home into a septic tank or city sewer system that is located under the ground level of the house. The term “blocked sewer line” is used when two or more pipes within the system are blocked. 

Let’s take a look at what can be the cause of this problem:

  • Plant roots in your yard have penetrated pipes.
  • The object fell into the toilet bowl, and someone accidentally flushed it.
  • The chemicals used to clean the bathroom fixture contain too much sulfuric or acid, which causes cracks in the pipes.
  • Someone has flushed the toilet with too many wipes or toilet paper at once.
  • Tectonic disturbances in your district have shifted ground levels and, thus, the position of your pipes.
  • A thicker layer of oily shampoo or soap has accumulated in the pipes.
  • If the pipes of the water system have not been changed for decades, there is a possibility that their structure is collapsing.

3. There Is A Blocked Vent System

Every plumbing system works at the same principle. While the wastewater, in this case, always moves downwards (under the foundation of the house), the excess air and gases go out upwards through the vent pipe that is usually located on the roof of the house. When the vent pipe is not working as it should, the plumbing system in your home will not work properly, and you’ll hear gurgling from your sink.

Clogging of the vent pipe is most often caused by piles of leaves, bird’s nests, branches, small animals stuck in the pipe, small objects like balls that have strayed onto the roof, and garbage that has been blown onto your roof by the wind.

Dangers Of A Blocked Vent System

A blocked vent system in the household is very dangerous for human health. The basic task of the vent is to bring clean air into the plumbing system’s pipes and to ensure adequate water pressure in the pipes with the airflow.

If the vent is blocked, there is no more clean air flowing. Gases and the unpleasant smell of sewage remain in the pipes, and they begin to spread through your home! The consequences are very serious and include nausea, severe headaches, dizziness, rapid heartbeat, and short/rapid breathing!

Related Article: How Much Does a Toilet Installation Cost?

4. There Is A Blocked or Damaged P-Trap

A gurgling sound in the sink that is created when flushing a toilet can also be because of a P-trap. It is a P-shaped water pipe that is located under every sink and has the purpose to prevents unpleasant odors from the sewage system from entering your home.

When, along with gurgling, you also feel the distinctive smell of sewage, you should check your P-trap. If you have basic plumbing knowledge and the required tools, you can fix this problem by yourself. But when the P-trap is inside the wall, a professional is recommended to do it for you.

This video might help you understand this problem better:

Regular Maintenance Of Your Home Vent System

To ensure that the vent in your home is always in good condition, you must regularly check the main vent opening, which is usually located on the roof of your house. All the gas and smelly air from the entire water system of the household ends up in that opening. You should pay special attention to the regular inspection of the outdoor vent unit if there is a tree above it.

The air that comes out through the vent on the roof in the main vent line comes from a series of smaller drains since every fixture through which water flows in the household usually has its own air drain. You should know that vent blockage is more common in cases where two fixtures share an air outlet, and thus also a problem in case of blockage. So, for example, gurgling in the sink can mean your toilet is clogged.

How to Fix A Gurgling Sound From Your Sink?

Fix A Gurgling Sound From Sink

If you are skilled in DIY projects, you can solve some of the most common causes of gurgling in your sink. Gurgling usually means that the balance between water and air circulation in the pipes is disturbed. In many cases, expelling the air stuck in the system will solve your problem. Checking the P-trap and squeezing the air out of it can take a long way. You can easily do this by filling the P-trap with water.

After an empty P-trap, the most common cause of the gurgling sound is a clogged vent system, which you can unclog yourself with the help of a plunger and apply the appropriate technique. The key is not to use force but to create a seal at the drain opening and then apply pressure with a moderate push.

Problem With The Main Vent

When the plumbing system in the house is poorly executed, plumbers often install a cheater valve (i.e. a valve for air admittance), in addition to the P-trap. A gurgling sound can also mean that this valve is worn out and you need to replace it. A new valve can be bought in any hardware shop at an affordable price. You can install it yourself, but if you are unsure how to do it, call a plumber.

We have already mentioned how a blockage of the main vent can cause a gurgling sound. After you have tried to solve the problem with the help of plunging and have not succeeded, inspect the outlet vent unit and, if necessary, clean it thoroughly.

Including vent protection, if you have it. First, remove with your hands everything that is visible and could potentially disturb the operation of the ventilation. Then rinse the main vent line from the highest point down with the help of a garden hose. You will recognize that the main vent line has been cleaned when there are no more bubbles in the return water.

For those who want to learn more, be sure to read Can Plunging A Toilet Damage The Wax Ring?

FAQ: People Also Ask

Why does my bathroom sink keep gurgling?

Gurgling in the bathroom sink is a sign that there is a blockage in the plumbing system that has trapped air. The presence of air in the water causes bubbles, and the movement of the bubbles through the pipe creates a loud, gurgling sound.

What happens if you don’t fix a gurgling sink?

Any blockage in the plumbing system should be repaired immediately. If you don’t fix the gurgling from your sink, the problem will only intensify, and the repair will become more difficult and expensive!

Why do waste pipes gurgle?

A gurgle can be heard from any type of pipe within the plumbing system when the balance in air and water circulation is disturbed. The balance is usually disturbed by the appearance of air in the water, i.e. the formation of bubbles whose movement in the pipe is heard as gurgling.

How to ensure that your home has an effective plumbing system?

All fixtures in your home that are connected with the plumbing system should be sealed, except for the toilet. That way, when a clogging problem occurs, you can solve it quickly and easily with the help of plunging. The key to the success of plunging is the creation of pressure that removes the cause of the blockage from the water system. If all ports but one are sealed, proper pressure will be easily generated.

Final Thoughts

If you have noticed a gurgling sound in your sink during toilet flushing, you probably have a clog in your household plumbing system that prevents proper air circulation. Air trapped in the pipe produces a gurgling sound. The problem should be solved immediately. If you ignore it, the clog will grow bigger, and eventually, the water flow in your house will stop. It is recommended that you hire a plumber for this task, but if you have basic plumbing knowledge and tools, you can try to do it yourself with a great deal of caution.

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