What Causes a Toilet to Bubble

There are many unusual sounds a toilet can make. Sometimes, it may even seem like the toilet flushes on its own in the middle of the night. One issue, when the toilet begins to bubble, can be particularly frustrating.

Toilets can bubble at any time. You may hear bubbles when taking a shower or using the sink in the bathroom. Some toilets may bubble on their own periodically, even when not in use. What could be causing such an issue?

The most common reason for a toilet to bubble is to have the primary drain in the bathroom experience a restriction.

Why Do Toilets Bubble When Drains Are Restricted?

When you are using water, either when taking a shower or using a sink, then it proceeds down the drain. If there is a restriction in the drain, then the water cannot move fast enough through the plumbing system. It will begin to backfill in the pipe, which means any air pressure caught in the pipes must be forced upward somewhere.

Sinks, tubs, and toilets all have traps in their plumbing design to prevent sewer gases from filling the bathroom. In the average bathroom, however, the toilet’s trap is above the floor. The sink’s trap is above the toilet’s trap. The tub’s trap is usually below the floor.

That is why when a toilet does bubble, there’s a good chance that you’ll be seeing the bathtub begin to back up with water – especially when using the shower. The air has already been pushed out of the bathtub trap and now it is moving through the toilet trap.

If water continues to flow into the drain that is partially restricted, the toilet bubbling can lead to the toilet overflowing.

To fix this issue, it is necessary to remove the obstruction. A toilet auger may be able to reach the obstruction, depending upon the structure of the bathroom. A longer plumbing snake may be able to reach the obstruction as well. If neither option works, then the only remaining solution would be to contact a professional plumber.

What Else Could Cause a Toilet to Bubble?

Although it is often overlooked, the modern bathroom is equipped with a DWV system. That stands for “drain waste vent.” It helps to remove the waste and gray water from the building. The focus is placed on the drain and waste component, while the venting component is ignored.

A DWV system must maintain a neutral air pressure in the drainage system of a home to allow the water and waste to flow freely and out of the building with an assist from gravity. Most homes use a downward slope to provide extra gravity power, but some use a grinding lift ejector pump.

Without the neutral air pressure, the water and waste cannot move as it should. This creates blockages, obstructions, and may even cause the water to backup into the tub and toilet over time. If such an event occurs, the air pressure within the plumbing system will be forced out into the toilet before the water backs up into it.

That causes the toilet to bubble as well. If the vent for the bathroom has not been sized properly or it becomes clogged for some reason, then the outcome can be a toilet starting to bubble unexpectedly.

The vent stacks for the DWV system are usually located on the roof. If the stacks are not covered properly, they can become blocked by falling debris, such as falling leaves, and that can prevent air from flowing through the system properly. Once the debris is removed, the issue with the toilet bubbling may resolve on its own.

The Issue May Be Outside the Building

If there is a blockage in the main sewer drain, the end result can be a toilet that begins to gurgle. In this scenario, the air backup occurs within the main pipe that serves a neighborhood or even an entire community. Every home connected to that main pipe would experience the bubbling issue in the toilet to some extent.

In this scenario, it would be the public utility that would need to fix the issue.

A similar problem can occur when there is a blockage associated with a septic system. If the water and waste cannot proceed through the system as intended, then the air pressure can back up into the toilet.

In many instances, the problem causing the bubbling can be fixed with a simple snake or by removing an obstacle or obstruction. If the issue cannot be identified or there is evidence of gray water backing up into the system, then contact a professional plumber as soon as possible.

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