Toilet Bubbles when Tub Drains: Causes and Fixes

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Having a fully functional plumbing system is one of the top priorities in every household.

But, when a problem occurs that relates to plumbing, most of us actually don’t have a clue what happens or how to deal with it.

That is exactly the case when your toilet bubbles when the tub drains. Now, this is not a common problem, but it is definitely a serious one.

In that light, let’s see everything that you need to know about this problem, and how to find a solution.

Toilet bubbles when tub drains

What Causes a Toilet to Bubble when the Tub Drains?

If you are not familiar with the term ‘’wet venting’’, it is a phenomenon that results in your toilet bubbling.

Simply put, every drainpipe inside your plumbing system requires separate venting or it might get clogged.

This is extremely important because if drain pipes are not vented separately, the pressure build-up will create numerous problems inside your plumbing system.

But, there are households that have a bit less functional plumbing systems and therefore have several drains close to one another. That’s why one vent is facilitating multiple drain pipes.

So, what exactly happens if you have this configuration? Well, when the vent is blocked, your toilet drain will start bubbling because the air is forced to exit there.

This all happens due to the fact that the water is entering a bathtub drain and that forces the air to leave in the toilet bowl.


Also, you might notice that other fixtures inside your bathroom are slow when it comes to draining. This also applies to your toilet bowl.

So, if the toilet is slowly draining and there are bubbles when you use your bathtub, the only logical thing to conclude is that your plumbing is not fully functional.

Therefore, it is probably a blocked vent that creates a pressure difference and that’s why air creates bubbles inside your bathtub.

Other Reasons

As we already said, the main reasons why your toilet bubbles are because the air is leaving the toilet drain because of the pressure difference that comes from your bathtub.

So, what else can cause this pressure difference aside of blocked vent?

Well, there are some reasons why the pressure difference is present inside your plumbing system. Let’s see.

  • Bad Pipes

If you have bad pipes inside your plumbing system, it is definitely a matter of time when some problem will occur. And, as we can see, toilet bubbling is one of those problems.

So, pipes inside your drain system should be made out of PVC and they should all be an appropriate size. But, if you have oversized pipes, then the air will have a lot of space inside the pipes and that will cause low pressure.

In that case, there just won’t be enough pressure to push the water and the air through the pipes and your plumbing system will certainly collapse after some time.

This is also important since there is a lot of water coming through the bathtub drain and that can cause air to leave the system in your toilet bowl. 

On the other hand, there is a problem when you have too small and narrow pipes. In that case, the water flow will be faster and stronger due to the high pressure that small pipes create.

This will also force the air to leave inside your toilet bowl and that’s why you hear your toilet bubbles.

  • Poor Connection

In case you have good pipes, you might be experiencing a poor connection between the pipes. Namely, toilet and bathtub are connected with usually one drain pipe that leads all the water down the sewage.

So, if the connection between that pipe and the toilet is loose, you will have your toilet bubbling.

Also, if the connection between the main drain pipe and the bathtub is loose or poorly installed, that will result in toilet bubbles as well.

This is because the bathtub is the lowest possible fixture, while the toilet is next in line since the sink is the highest fixture inside a bathroom.

toilet fills up then drains slowly

How to Fix a Bubbling Toilet

Now, there are some solutions that can solve this kind of problem, but, we strongly suggest that you consider getting a professional for this kind of job.

Anyhow, if you decided to give it a shot with your own two hands, here’s what you can do:

1. Completely clear the bathtub drain

A bathtub drain is usually the place that gets clogged the most inside our bathrooms. That’s why it creates a lot of problems like toilet bubbling.

Anyhow, you will need to clean all hair and soap build-ups inside the bathtub drain and remove everything that got stuck down there.

You might like: How to Clear a Clogged Tub Drain Naturally (No Chemicals!)

Pro Tip

clog tub

We recommend you check out the Clog Demolisher. It uses high pressure air to naturally unclog your sinks and tubs, without the need for harmful chemicals.

Just pump the air and press the trigger. It's so simple and it helps you save on plumber's fees!

2. Clean the vent

If your plumbing is fine, then you are experiencing a problem with the vent, which is usually the worst-case scenario.

Now, you will need to access the vent through the roof and see if there are any leaves or dirt build-ups inside that vent.

Clean everything nicely and you might solve the problem.

how to unclog a shower drain

3. Clean the main drain pipe 

Same as the bathtub pipe, the clog could be located inside the main drain pipe. Now, unclogging this one is a pain in the neck since you will need a lot of tools and special mixtures to get it cleaned.

Anyhow, try using a plumber’s snake through the bathtub and you just might locate the clog and remove it.

Conclusion: Toilet Bubbles when Tub Drains

Toilet bubbling is a sign of the problem that occurs inside your plumbing. That’s why you need to fix it immediately. And, as you can see, we have explained everything that can lead to toilet bubbling when you use your bathtub drain.

Now, locate the problem and find a proper solution since toilet bubbling will continue and progress into something far worse.