Why Does My Toilet Bubble When the Bathtub Drains (5 Possible Fixes)

Plumbing is a very important part of the home that we rely on a lot, so it’s alarming when it isn’t working the way it should. If you notice that your toilet is bubbling, it indicates problems with the plumbing that need to be addressed right away.

The most common reason a toilet bubble when the bathtub drains is a clogged bathtub drain. Another possible reason is a blockage in the vent stack. There are commercial products designed to clear these blockages and methods using natural products.

It is not too uncommon for a toilet to bubble because of plumbing issues. In fact, all plumbing systems will have problems at some point, and there are effective ways of repairing these problems.

We will go over the reasons your toilet is bubbling, how to troubleshoot, and how to fix these problems.

If you’ve never dealt with this problem, there’s a chance that you don’t know what signs to look for.

How To Tell If Your Toilet is Bubbling?  

Fill the bathtub about a quarter of the way, then allow it to drain. Now pay attention to any changes with your toilet. Are there small bubbles in the toilet water? Is the toilet making a gurgling sound?

If either of these things are happening, there’s a chance that you have a problem with your plumbing. We will discuss the two most common reasons behind a bubbling toilet, and how to fix those problems. 

These repairs are relatively simple, and seldom require a professional. However, if these easy fixes don’t work, it could indicate a more significant problem with the plumbing system. Poor connections between pipes, mineral buildup, and a problem with the main drain pipe are possible culprits, and these problems are best addressed by professional plumbers.

Now that you’ve determined that your toilet is bubbling, it’s time to figure out why. Here are the two most common reasons why a toilet bubbles, why this happens, and what step to take to prevent these problems.

Common Reasons Why Your Toilet Bubbles 

Your Bathtub Drain is Clogged 

The most common reason behind a bubbling toilet is a clogged bathtub drain. This is because the bathtub and toilet (and even your washing machine drain) often share a drain that leads to the house’s main drain pipe. 

When the bathtub drain is blocked, this creates negative air pressure in the tub and toilet’s shared drain. This air has to go somewhere, so it is forced up through the toilet. This air will appear in the form of bubbles, or gurgling sounds from the toilet.

It’s usually easy to tell whether your bathtub drain is blocked. If it drains slowly, that usually indicates that there is a clog somewhere in the bathtub drain pipe. To double check, remove any visible hair or other debris from the drain. If it’s still draining slowly, your clog is in the drain pipe.

Clogged bathtub drains are a common problem, and are caused by hair and toiletries that build up in the drain. While it’s usually an easy fix, they can be prevented by using hair traps and the occasional use of commercial drain unclogger. 

The Vent Stack is Blocked  

Behind a clogged bathtub drain, a blocked vent stack is the second most common reason behind a bubbling toilet. This is because the toilet and bathtub usually share a vent stack, in addition to a common drain.

A vent stack is a pipe that is connected to the tub and toilet’s shared drain. This pipe removes sewer gasses from the shared drainpipe so wastewater can flow into the sewer system. 

The part we see on the roof is the end of this vent stack, which releases the sewer gasses. When this part of the vent stack gets clogged with debris like leaves, pinecones, and twigs, the gasses aren’t allowed to escape. Since air has to go somewhere, it is usually forced back through the toilet.

The best way to check for a blocked vent stack is to do a visual check. If you’d rather not get on the roof if you don’t have to, there are signs to check for. If your toilet is bubbling or gurgling, and the bathtub is draining normally, there’s a good chance that your vent stack is the problem. 

Like a clogged bathtub drain, this repair is relatively straightforward. If you would like to get ahead of the problem, there are a couple of preventative actions you can take. Trimming tree branches and capping the vent stack are both effective at keeping debris out.

Best Fixes For Your Bubbling Toilet

Simple clogs are a very common problem. At some point, it is almost certain that every plumbing system will have a blockage. Luckily, there are products and procedures designed specifically to clear blockages. Here are the most common and effective ways to clear drains and vent stacks.

Use a Commercial Declogger to Clear Your Drain

The most common way to clear clogs from bathtub drains is by using a commercial chemical declogger. There are three types of chemical decloggers on the market: caustic, oxidizing, and acid-based, and they all do a good job. 

While these are all effective products, it may not be a good idea to use certain chemicals with a septic tank. If you’re on a septic tank rather than a sewer system, just make sure to use a declogger specifically for septic systems.

As with any commercial product, check the directions before using the declogger. The directions don’t typically vary widely between manufacturers, but it’s always better to be safe.

Start with ventilating the bathroom by opening a window or turning on the exhaust fan. Remove the drain stopper and check for visible clogs. If you can see hair or any other physical blockage, remove as much as you can.

After you’ve cleared the way as much as you can, pour the manufacturer’s recommended amount of product directly into the drain. Wait the amount of time listed in the instructions, then flush the drain as directed.

Large clogs may need a second treatment, but as we mentioned before, always follow the manufacturer’s instructions.  

Use a Natural Solution To Clear Your Drain

If you prefer to avoid harsh chemicals in commercial decloggers, or you’re on a septic tank, you can use natural products to clear clogs. These natural products are common household items that you probably already have on hand.

The most common natural drain declogger is baking soda with a vinegar rinse. This combination creates a chemical reaction that in turn creates pressure that breaks up and moves blockages.

As with a commercial de-clogger, try to manually clear any visible blockages. Pour 8 cups of very hot water into the drain to melt toiletry buildup. Once it drains, pour in ½ cups of baking soda, and let it sit for a few minutes.

Now mix 1 cup of hot water with 1 cup of vinegar, pour this mixture into the drain, and let it sit for 10-15 minutes. Pour another 8 cups of very hot water into the drain. You may need to repeat the treatment a couple of times to remove the blockage. 

Use a Bathtub Snake 

If you’ve tried a drain de-clogger and the bathtub still has problems draining, the blockage has to be removed manually. A bathtub snake is designed specifically for this job.

Before you get started, it’s a good idea to wear gloves to protect your hands, plus eye protection to protect you from splatter.

The snake can go through either the bottom drain or overflow drain, this is up to you. Depending on which route you choose, remove the stopper or overflow drain cover. 

Now feed the snake cable into the drain. When your cable stops, you’ve hit the clog. Turning the handle clockwise, push the cable through the clog, then pull the clog out. 

Watch for splatter as the clog comes out-this is where eye protection comes in handy. Run water to make sure normal drainage is reestablished. If it still drains slowly, you can try again with the drain snake or with a declogger.

Use a Plunger to Clear the Bathtub Drain

This method is very straightforward, but not as effective as the commercial decloggers or drain snake. 

Before getting started,make sure to use a plunger designed for bathtub drains, because a toilet plunger will not work. A toilet plunger does not have the right base to form a tight seal around the bathtub drain.

Fill the tub with enough water to cover the base of the plunger, then position the plunger around the drain. Give 12 strong downward pushes on the plunger. Repeat until the water drains normally.


Clear the Vent Stack 

If you already know that your tub is draining normally, you can skip the drain unclogging process and go straight to the vent stack on the roof. It’s best to have an assistant for this, not only to help check whether the blockage is gone, but as a safety measure as well.

Before you get up on the roof, make sure you have everything that you need. Grab a flashlight, a plumber’s snake, and a garden hose to flush the vent stack.

To get started, get on your rooftop safely. If your vent stack has a cap, remove the cap and set it aside. With your flashlight, look into your vent stack to try to locate the blockage. 

If you can see all the way down clearly and there is no blockage at all, your vent stack probably isn’t the problem. In this case, it might be best to consult a professional plumber, since the problem is likely deeper in the system.

When you locate the blockage, feed the plumber’s snake into the vent until it breaks through the blockage, then pull the blockage out. Flush the vent with your hose to dislodge any remaining debris. 

Have your assistant flush the toilet inside, and hold your hand over the vent. If you feel suction, the job is done. If this isn’t the case, do the toilet bubble check we discussed before. If the toilet still bubbles, it’s probably time to consult a professional plumber. 

When You Should Call a Professional

There are situations where it’s best to call a professional plumber for help. If DIY fixes haven’t solved the problem, or you live in an old home, the problem might run deeper in your plumbing system.

Some repairs require the removal of fixtures or access to pipes, which can create a lot of additional work. Professional plumbers have the equipment and training to perform this type of work, and they can troubleshoot deeper problems with your system. 

Problems like bad pipes or poor connections are best addressed by professionals, as they often offer guarantees on their work. Whatever the problem turns out to be, it’s never a bad investment to hire a professional plumber. 

How Much Does it Cost To Fix a Bubbling Toilet?

If you feel confident that the problem causing your toilet to bubble is a simple clog, you might be considering whether it’s worth it to hire a professional. 

For simple blockages, it is definitely more economical to do the repair yourself. However, if the problem runs deeper and requires extensive repairs, it is necessary to hire a plumber. 

It is difficult to put a price point on pipe replacements, however. Depending on the extent of the problem, it can cost anywhere from $150 for a single pipe to $20,000 for an entire new system. 

Hopefully, it’s just a simple clog that needs to be addressed. Here’s a cost comparison so you can see the difference between doing this repair yourself and hiring a professional. 

DIYProfessional Plumber
Unclog Bathtub Drain$6 – $30$200 – $250
Clear Vent Stack$10 – $30$100 – $200


Blockages in the bathtub drain or vent stack are the most likely culprits behind a bubbling toilet, and luckily there are easy fixes for these problems. These DIY fixes are straightforward and economical, plus they are great for getting familiar with your plumbing system.

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