A bubbling toilet when the shower is running is a curious phenomenon that should interest any homeowner. Unfortunately, it is a much more prevalent problem that many homeowners cannot resolve.
Like most people, you don’t want to think about what is happening in your restroom behind closed doors. But it’s difficult to ignore if your toilet starts bubbling when you shower, empty the bathtub, or use the bathroom sink.
When a toilet gurgles, it means some airlock develops in the drain line due to the buildup of negative air pressure. In a drain system that is working properly, air flows easily through the pipes, preventing negative air pressure and allowing waste to flow down and out without any problems.
However, bubbling is a sign of irregular suction developing in the line. After a while, the negative air pressure will let go, forcing air into the toilet bowl and through the drainpipe. When this happens, you may hear the toilet bubbling, see bubbles in the toilet bowl, or even hear the toilet flush itself.
Why is My Toilet Bubbling When the Shower is Running?
- Clogged Venting System
The water in your toilet may be forced out by a continuous air cycle brought on by a clogged vent. An air vent that sends air into your home for ventilation extends from the main drain or sewer line.
Clogging in the venting system can be caused by leaves, dirt, and twigs. When this occurs, the air cannot escape, and more air is forced in until insufficient pressure forces the air out of the toilet.
Until you clean or replace the vent, the low air pressure will cause your toilet to bubble each time the shower runs. Since the vent stack is a critical component of your complete plumbing system, issues with it will cause problems elsewhere. 
Check to determine whether the water flows properly in other sinks, bathrooms, or hose connections. You might observe:
- Other drains or toilets are gurgling.
- Water drains slowly.
- Sewage stink emanates from drains when there is no water flowing.
- Drains that keep backing up even after you clean the obstructions
- Clogged Sewer Line
A blocked sewer line has a similar impact as a clogged vent. When you use the shower, bath, or sink, you may hear gurgling and bubbling in the toilet due to a blockage in your mainline, commonly referred to as the stack .
This problem develops due to garbage accumulation inside the pipes, tree roots encroaching into your lines, incorrect installation, or inadequate pipe sloping. For example, when someone takes a shower, a blocked drain line may force the water out of your toilet.
- Clogged Drain
Your drain pipes being blocked by something is one of the main causes of your toilet bubbling. If your drain is partially blocked, you’ll see that the bubbling has just started.
Even though you might not think this is a huge concern, leaving your drain in this condition could entirely clog it. Your drain may be plugged if water isn’t flushing down the toilet anymore. Dirty hair, dead skin, soap residue, clogged wipes, oils, grease, and fat are some causes of blocked drains.
Read Also: Toilet Flushes But Waste Come Back
If you’re not experiencing any other problems, the toilet pipe is to blame. Your toilet is notably bubbling, and that you are aware of it is a good indication that your primary issue is related to the toilet drain.
The likelihood of the problem in (or very near) your toilet is very high if there are no other plumbing-related symptoms. Your shower drain line is likely blocked and forces air through the adjoining bathroom. However, you would probably first notice that the water in the shower is draining slowly.
- Faulty Plumbing
Faulty plumbing installations may cause water to burst out of your toilet even though your mainline is in good condition and the sink or shower drains normally. Gurgling toilets are caused by poor installation or damaged grade lines. 
For instance, if your sewage line is not correctly graded, it will fill with water and clog, which might result in bubbles every time the toilet is flushed. You will need a plumber to do a camera check on the sewer line to identify the problem’s root cause and make a long-lasting repair.
- Clogged Water Main
If your neighbors are also experiencing the bubbling toilet problem, the water main is definitely to blame. Call your neighbors and inquire if they are experiencing any strange plumbing problems.
If there is, there may be a problem with the sewage main in your block. Contact the water management division of your city to report the problem. There may be a blockage in the main sewage pipe, a general issue with the city’s water system, or a broken sewage pipe.
Fixing the toilet bubbling problem
- Plunge your toilet to find a quick remedy
Tape over the drain in your shower, or insert a towel within the opening. Then plunge your toilet for 1-2 minutes as though it were clogged.
After that, try turning on the shower to see if the bubbling stops. You could be lucky and be able to solve it with a fast plunge if it was only a little obstruction.
Because you’ll artificially boost the pressure in both the toilet and shower, covering the drain is crucial. The plunger now has the leverage it would typically require to drive the obstruction down.
The barrier must be close to the surface for plunging to be effective. You can skip this step if your toilet is bubbling due to a blockage further along the line.
Plunge your shower drain after you’ve done the toilet. Continue plunging if you still hear bubbles while your shower is running, or continue to the next step.
- Use a drain auger to snake the toilet.
Cover the shower drain with duct tape or block the opening with a towel. Next, place the end of a drain auger in the toilet bowl.
To move the snake down the pipe, turn the handle of your auger. Continue until you encounter opposition and identify your roadblock.
Once the blockage has been released, extend your snake and push the auger’s end a little more.
If the issue continues, try snaking your shower drain. The pipe may be where the obstruction is located. However, if you fully extend the snake and encounter no resistance, the issue is likely somewhere else.
- To unblock a clog in your vent stack, hire a roofer.
Inform a local roofer that you believe there is a blockage in your vent stack (or if you can find one, a plumber with a roofing license). They’ll climb onto your roof and either snake the pipe or take care of the issue themselves.
If your roof is flat and you have access, you can snake the vent stack yourself. If you’re on the flat top, bring a flashlight and search the vent pipe.
If you can reach inside, clear the obstruction. If not, use a drain auger to snake it like a regular drain. To assist in clearing obstacles deeper down, remove debris and splash water down the vent.
Use a plumbing auger to clear up persistent obstructions if the vent overflows. Once cleaned, consider covering the plumbing vent with a safety screen to avoid a recurrence.
- Use Chemicals
Pouring drain cleaning agents down the shower drain is one alternative. But it is not advisable because doing it repeatedly can damage your plumbing. Additionally, all those chemicals will be going into the water supply.
Using salt, baking soda, peroxide, or safe enzyme-based cleansers is preferable. You can also utilize a longer plumbing auger to reach further into the plumbing system.
Read Also: Does Bleach Damage Toilet Bowls
- If the water main is the main problem, get in touch with your city management
You won’t be able to repair any problems with the sewage system in your city because there aren’t any commercial drain augers that can reach that far. And you won’t be able to remedy the issue most of the time, anyway.
Instead, contact your local water agency to report an issue. They’ll dispatch a team to examine your sewage pipe.
- Call a Plumber
If your toilet is bubbling and you’re having trouble clearing the pipes, you can always call a licensed plumber for an expert drain. A skilled and experienced plumber is the best person to help you if you have obstructions in your drain.
The same holds when cleaning out a vent stack. Again, the best action is to hire a licensed plumber to remove the block for you. This is not a job you should try to accomplish if you can’t securely get onto your roof.
It’s also conceivable that the bubbling is brought on by another plumbing issue that may be more serious. Therefore, it’s always a good idea to have a qualified plumber take a look to avoid a greater problem down the road.
Your toilet is bubbling because of an issue with the drain line, which is where the problem is. This problem needs to be addressed since it frequently worsens over time. It may also result in your bathroom losing all functionality and maybe having a terrible sewage backup.
Although there are a few things you may do that quickly address this issue, it’s usually best to leave determining the problem and repairing it to the experts.