Toilet Bubbling When Flushed? Here’s What To Do

A bubbling toilet makes your kids laugh, but the possible causes aren't so funny. You can fix many of the causes yourself, but a few require a pro.

Does your toilet bubble or gurgle when flushed? While it may not seem like a critical problem, it is a sign that something is wrong with your plumbing system and it needs to be fixed. I talked to two licensed plumbers, Alexander Siv and Jason Duda, to help explain the causes of a bubbling toilet, when you can fix it yourself and when to call in a pro to remedy this puzzling plumbing issue.

What Causes a Toilet to Bubble When Flushed?

“A gurgling toilet usually means there’s a clog in the drain line or there’s an issue with the plumbing venting system,” Duda says. “There’s not enough air in the system so when the water goes down the drain it’s sort of gulping for air as its goes.”

Here are some situation that can cause a toilet to bubble when flushed, as well as ways to fix each issue.

Clogged toilet

A clog in the toilet’s trapway (the curved part of the toilet base near the back) is one of the more common causes of bubbling or gurgling. It can be the first place clogs occur due to excessive toilet paper, solid waste or flushed non-biodegradable paper products.

The fix for this is usually DIYable. Position a toilet plunger over the toilet bowl outlet and do 10 to 15 vigorous plunges. If the clog is in the trapway or anywhere near the toilet itself, this should dislodge the clog and solve your problem.

If a plunger doesn’t work, try a toilet auger. Wearing protective gloves, insert the auger end into the toilet bowl and into the drain pipe without scratching the porcelain. Turn the auger until you hit pressure, then retract the auger line and (hopefully) your clog.

Clogged vent pipe

Every plumbing fixture, including toilets, is connected to a vent pipe that extends through the roof and provides air to the drainage system. If these vents become clogged, you’ve got a problem.

“[Vents] provide air to the drainage system and allow the water to go down the pipes,” Duda says. “If the vent pipe is blocked or clogged, this can lead to gurgling or bubbling in the toilet.”

Outside, vent pipes can get clogged with bird nests or debris from hanging branches. Inside the home, a blocked drain line can redirect flushed paper up into the vent pipe, causing a clog. This is a common issue encountered by Siv. “The water recedes, and the paper hardens in the vent,” he explains. “Even a partial block will restrict the airflow and can lead to a gurgling toilet.”

You’ll likely need a pro to fix a clogged vent pipe. Pros send a camera down into the vent pipe from the roof to locate the clog. Then they use a drain auger or snake to remove the blockage.

“If I can see it on the camera, I can normally get it with the snake,” Siv says. If not, this means the clog is in a horizontal pipe behind a wall. To find and fix these clogs, he cuts an access hole in the wall to gain entry to the pipe.

If you want to try to unclog your vent pipe yourself, get a length of rope, a thin flashlight and duct tape. Wear rubber-soled shoes and plan to do the work when your roof is dry. Locate your vent pipe and carefully climb up to your roof on a properly secured ladder and wearing a roof safety harness. Tie and tape the flashlight to the rope, then lower it into the pipe.

Look for debris and use a drum auger to retrieve the blockage. Send the tip of the end of the flexible wire into the pipe and turn the crank handle each time you extend more wire. If you hit resistance, turn the handle a few times to break up the blockage, then retrieve the wire (and blockage) from the pipe. When finished, pour water down the vent to clear any remaining debris.

If your roof is steeply pitched or more than 12 feet from the roof edge to the ground, sty safe and hire a pro.

Blocked drain line

Clogs in nearby shower or tub drains can also cause bubbles in the toilet when a toilet is flushed. “This is more likely if the clog is located near the drain vent and is blocking air flow,” Siv says. This can lead to the system pulling air from the toilet bowl, causing bubbling. A clogged drain line can also trap air in the system that will escape out the toilet bowl and cause bubbling.

The fix for this is to use a plunger or drum auger to remove the clog in a nearby shower or tub drain. And here’s another chemical-free way to remove clogs in a shower or tub drain.

Clogged sewer line

A clog or partial blockage in the main sewer line can also cause air to become trapped in the pipes. When you flush a toilet, the trapped air can create bubbles or gurgling sounds in the toilet bowl.

Other signs that indicate a block in the sewer line is a foul smell in your bathroom or if flushing one toilet causes another to bubble. “If you’ve got a toilet that is gurgling you might have other fixtures that are gurgling, which can point to a sewer line issue,” Duda says.

Sewer lines can become blocked by tree roots, a damaged pipe or debris buildup.

“It’s a good idea to call a drain cleaning company and have them snake out the lines,” Duda says. Sewer and drain professional use cameras and extended electric augers to remove the clog. If the problem is tree roots or a damaged pipe, a pro can diagnose and repair the problem.

Maintenance Tips for Prevention

    • Address minor clogs promptly. Unclog a slow-draining toilet promptly to prevent bigger backups.
    • Flush only toilet paper and solids. Avoid flushing sanitary products, baby wipes and tissues as these are not intended for use in a toilet and can cause clogs.
    • Trim back overhanging branches. Prevent debris from making its way into vent pipes and creating a clog. If trimming isn’t possible, consider placing a vent pipe screen to keep out debris.

About The Expert

Alexander Siv is the owner of Amherst Heating and Plumbing in Amherst, Massachusetts. He has a master plumbers license in Massachusetts and has more than 10 years of experience.

Jason Duda is the manager of Boulanger’s Plumbing and Heating in Easthampton, Massachusetts. He holds a master plumbers license in Massachusetts, Connecticut, New York and Virginia with 25 years of plumbing experience.

Laurie M Nichols
I am a freelance real estate writer, specializing in accessible and engaging content for websites in the industry. I draw on thirteen years of real estate investing experience, as well as seven years as a home repair professional to inform my writing. I am a former high school English teacher with a M. Ed in Secondary Education and am a registered Home Improvement Contractor in the State of Massachusetts.