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Why Does Toilet Bubble When Tub Drains?

You’re relaxing in your bathtub, soaking and taking every moment in after a long tiresome week. The peace and quiet is soothing, but suddenly, you hear a gurgling noise in your toilet. Upon looking closely, you notice that there are toilet bubbles when you drain the bathtub. Your relaxation session is over. Now you have to think about what’s happening. Could there be something wrong with the drainage?

In most cases, the toilet and shower share a drain and vent stack – a setup that’s known as wet venting. If you’re noticing bubbling when the tub drains, chances are you have a blockage. The only way to fix the problem is to have it repaired. However, there are some things to know before taking those steps. 

It’s never a good idea to ignore a plumbing issue. A bubbling toilet may not seem like a big deal, but it may be a precursor to a blocked pipe that may cause your entire bathroom to shut down. You don’t want it to get to this point because you’ll spend a hefty amount on plumbing fees. Here’s everything you need to know about toilet bubbling when the tub drains and how to fix it.

Why Does My Toilet Bubble When My Bathtub Drains?

If you’re asking this question, you’ve probably noticed the problem a couple of times, which means it’s a problem you shouldn’t ignore. But before we get into how to fix it, it’s crucial to know what may be causing the problem.

You’ll often find this problem in a bathroom where the shower and toilet share a drain and vent stack. This setup is known as wet venting. If any of these parts have a blockage or clog, air is forced up or down the toilet, thereby creating the bubbles and gurgling noises you’re hearing.

What is Wet Venting?

Drains are generally vented separately. However, if they’re close enough, like in your bathroom, the drain is vented through one pipe that acts as the drain for another fixture. If there’s a clog or blockage anywhere in this line, air is pushed out or sucked into one of the fixtures (such as the toilet), when another fixture is being used (bathtub).

Causes of Blockage in Wet Venting

Two things can cause a blockage in a wet venting drain setup. These include:

  • A clogged sewer drain
  • A blocked vent stack

Here’s a closer look at both problems and some of the signs you should keep an eye on to determine the exact problem you’re facing. 

Clogged Sewer Drain

If there’s a blockage in the drain, the gurgling noise could result from several factors. These include

  • Forcing air out: In a wet venting set up, when you turn your shower on, the water usually drains down the pipe as it pushes out the air that was there out with it. However, if there’s a clog, the air will be trapped and force its way out of another drain, like the toilet.
  • Sucking air in: In the presence of a clog, the flow of water from the tub to the sewer drain may create a vacuum. The vacuum effect is strong enough to suck the air down through the toilet p-trap, thereby causing a gurgling noise.

A gurgling toilet may seem like a nuisance you can easily ignore, but you shouldn’t. If the problem is not addressed, you may end up with bigger issues like damaged pipes. Such damage will create a dent in your wallet. Therefore, it’s best to take action as soon as you notice the bubbling and gurgling noises.

Blocked Vent Stack

As we’ve mentioned, in a wet venting setup, there’s a great chance your shower and toilet share a vent stack. If this is the case, the cause of the bubbling and gurgling noises may be due to a blockage in the vent stack.  The vent stack is put in place to:

  • Get rid of gases and sewer odors, thereby keeping your home smelling good and fresh
  • Bring fresh air into your plumbing system to maintain a proper atmospheric pressure, which aids in proper water drainage

While vent stacks don’t carry any water, they’re a crucial part of the plumbing system. If the vent stack is blocked, it can interrupt water flow and trap air in your pipes. Instead of leaving the vent stack, air is forced out of other parts like your toilet, thereby causing the bubbling and gurgling noises you’re hearing.

Source: Redcap Plumbing

Blocked Tub Drain

Various things like hair, soap, and debris can get stuck in your dub drain, thereby causing gurgling sounds in your toilet. Even if you use a hair trap for the bathtub every time you shower, some of the strands can pass through and accumulate over time. Combined with soap, this type of clog can cause a major problem if not fixed.

How Do You Fix a Gurgling Toilet?

The only way to fix a bubbling and gurgling toilet is to remove the blockage. Depending on where the clog is, there are several ways to go about it. Here’s how to clear out blockages in the different parts of your piping system to ensure smooth operation and your peace of mind.

Drain Line

Drain line clogs can occur anywhere past the pipe. You need a long drain snake to get rid of the blockage and get the air and water flowing as they should. We highly discourage using commercial drain cleaning products. These products are extremely harsh to the point that they can damage your pipes, or worse, enter into the public water supply.

If you have no experience clearing drains, trying to do it yourself is risky. You risk causing further damage, which may make repairs even more expensive. Therefore, if you’re not confident enough to take on the repairs, consider hiring a plumbing expert.

Vent Pipe and Stack

To clear a blockage in the vent stack, you’ll need to go up to your roof. Begin by locating the vent stack. It should be on the roof above your bathroom. Next, remove all the visible blockages like leaves and dirt that may be stuck at the very top. If the blockage is only on the surface, remove all of it and cover the vent with a protective screen to prevent future blockages.

However, if you suspect that the clog is located deeper in the vent, it’s best to contact a plumber instead. A professional will have the right equipment, and they’ll know how to get rid of all the clogs without causing further damage.

Tub Drain

The problem may also be caused by a blockage in your tub drain. You can tell by observing the flow of the water. If the drainage is slower, there’s a high chance it’s clogged with hair, soap, or other debris. To fix the problem, use a drain snake or Zip-it tool to pull or break apart the clog. Again, if you’re not sure you can do this yourself, call a professional.

Source: Reichelt Plumbing

Shower in Peace

Like a skeleton, the plumbing in your home is connected. A problem in one area can affect another and cause massive damage. Don’t let it get to this point, especially if you’ve started hearing noises and bubbling in your toilet. These signs signal a blockage, and if left unresolved, they can cause massive damage to your plumbing system.

Save yourself the headache and possible hefty plumbing costs in the future and get the problem fixed immediately. Remember, if you’re not experienced in fixing drainages, it’s best to leave it to the professionals lest you cause further damage.

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