Why Your Toilet Bubbles When The Bathtub Drains-Easy Fix

Last Updated on September 28, 2023 by toilethaven

Why Does My Toilet Bubble When I Drain My Tub?

A proper-function bathtub should not be in any “communication” with the toilet. When you notice your toilet bubbling/gurgling any time you drain your bathtub, then you need to fix it as soon as possible.

If your toilet bubbles when you drain your bathtub, it is a sign that the drainpipe or vent stack is clogged. This causes negative air pressure inside the drainpipe/vent, which is forced out through the toilet in the form of bubbles.

Although a toilet and a bathtub are independent fixtures, their drainpipes are joined together in the main house drainpipe. Due to their close proximity, they also share the same vent stack. A problem with one fixture’s drainage will directly affect the other fixture.

Think of a house plumbing structure like a tree. A tree has several branches and one trunk. Each branch represents a single fixture that drains into the main house drainpipe, in this case, the tree trunk.

Toilet Bubbles
Toilet bowl flush. Close up.

Clogged Drainpipe

If the main house drainpipe is clogged, you will definitely have a problem with all the fixtures. You might, therefore, notice that the toilet bubbles when flushed or:

  • The toilet bubbles when the washer drains.
  • The toilet is bubbling and won’t flush.
  • The bathtub drain gurgles when the toilet is flushed.

Since a vacuum cannot exist, the space in the drainpipe between the clog and the bathtub will be full of air. When you start draining the bathtub, the water will displace the air in the drainpipe.

The displaced air will force its way out through the bottom of the toilet bowl. This is the main reason why toilets bubble when a bathtub is draining.

Sometimes, the main house drainpipe is not clogged but just the one connecting the bathtub and toilet.

To ensure this, turn on the water in the sink and listen for bubbling from the toilet. If it bubbles, then sure enough, the main drainpipe is clogged. On the other hand, if it doesn’t, the problem is only with the tub and toilet.

Clogged Vent Stack

A vent stack is a pipe connected to the drainpipe and runs through the house’s roof. It removes sewer gases from the drainpipe, allowing waste to easily flow down the drainpipe and into the sewer lines or septic tank.

If the vent stack is clogged, sewer gases cannot flow out. Pressure will start to build up inside the vent, so when the bathtub is drained, water pressure will force the trapped sewer gases out through the toilet in the form of bubbles.

The water at the bottom of the toilet bowl is meant to prevent sewer gases from entering the bathroom. Due to the volume and pressure of the draining bathtub water, the trapped sewer gas pressure will breach the toilet bowl water barrier, resulting in a bubbling/gurgling toilet.

Why You Should Fix a Bubbling Toilet ASAP


If you are dealing with a clogged main drainpipe, waste from your bathtub, toilet, shower, sinks, or washer is not flowing into the sewer lines. It is accumulating in the drainpipe.

Initially, your toilet or other adjacent fixtures will only be bubbling or gurgling whenever you drain the bathtub. But things will not be that way for long.

As more waste accumulates in the drainpipe, it will run out of space, and a backup will be inevitable. A backup happens when sewage emerges from your toilet, sink, or any other fixture.

You might be safe if it is a partial clog because a backup is unlikely. The toilet will, however, continue to bubble each time the bathtub drains.

You should, however, still fix a partial clog as soon as it can develop into a full clog within no time. This will be a cheaper and easier fix.

A toilet that is backed up will cost you a lot of money. First, you are less likely to fix it yourself; hence, you will need to call in a professional plumber. Those are not cheap.

Don’t also forget the awful odor that comes with a house that has a backing-up problem. You might not even stay or sleep in the house until the problem is fixed.

How to Fix a Toilet that Bubbles when a Bathtub Drains

There are several ways to fix a toilet that bubbles/gurgles when a tub drains. The solution can be an easy or a very difficult and expensive one. It will depend on:

  • The severity of the clog.
  • The position of the clog.
  • The type of clog (material).

The following are the different ways to fix a toilet that bubbles after draining a bathtub:

1. Plunge the Bathtub

If you have a bathtub, chances are high that you also own a bathtub plunger. Here is you to properly unclog a bathtub using a plunger:

  • Remove your bathtub’s drain plug using a screwdriver.
  • Check (using a flashlight) if there are some obstructions that you can easily remove. This includes things like hair or soap scum.
  • Cut and straighten a wire hanger and bend it into a hook at the front using a pair of pliers.
  • Push the hook inside the tub drain and remove as much of the obstructions as possible.
  • Plug the bathtub overflow drain with a rag or towel to prevent pressure loss.
  • Place the plunger around the bathtub drain and turn on the hot water until the base of the plunger is covered with water.
  • Start plunging up and down without lifting the plunger above the water. Hopefully, this will dislodge the clog.

Lift off the plunger and let the water drain. Listen carefully if the bubbling from the toilet has stopped. If it hasn’t, then you will need to upgrade to a better tool.

You should avoid using chemical-based drain cleaners to unclog a bathtub or any other drain for that matter. Using hot water, baking soda, and vinegar is a better alternative.

The following video from Home Depot is very helpful.


2. Snake the Bathtub

A bathtub snake contains a handle, a flexible cable, and a hooked head. It acts directly on the clog inside the drainpipe. You can either buy your own snake or rent one out.

Introduce the snake slowly inside the tub drain as you crank the handle clockwise. When you encounter an obstruction, change the cranking direction, then crank again in the original direction until you go past it.

If you cannot go past a certain point, gently pull out the snake and inspect it. There is a chance that you might have hooked and pulled out the clog. The good thing is that due to its design, bathtub clogs are not as nasty as those found in toilets, and a snake will easily shred/pull them.

3. Plunge the Toilet

A toilet plunger is a must-have, even for people with the most powerful flushing toilets. It is very helpful in unclogging clogs that are not too far down the drainpipe.

Toilet plungers are a little different from other drain plungers. Unlike other drains, the toilet bowl outlet is not a flat surface; hence, other plungers won’t do the trick. The best toilet plungers are bell-shaped.

The bell-shaped toilet plunger allows you to make an air-tight seal around the bowl outlet to prevent pressure loss. If you want to learn how to plunge like a plumber, check out this post.

4. Snake the Toilet

A toilet snake, also known as a toilet auger, is about 3 to 6 inches in length. Like the bathtub snake, it acts directly on the toilet clog by shredding it into small pieces or hooking it and pulling it out.

Toilet augers are more powerful than tub snakes and are more reliable in removing stubborn clogs, especially those further below inside the drainpipe.

For even more stubborn stains, you can buy or rent out a longer motorized toilet auger. Home improvement stores like Home Depot offer such services.

The main challenge in using a toilet auger is that you can easily and badly scratch the inside of your toilet bowl, leaving it with very ugly marks. If you would like to learn how to properly unclog a toilet with a toilet auger, check out this post.

5. Unclog the Vent Stack

Before calling in a plumber, you should first ensure that your vent stack is not blocked. Since it is normally open at the top to allow sewer gases to flow out, the vent stack can easily be blocked by tree leaves, dead animals like birds and rodents, or even snow.

Use a ladder to climb to your house’s roof and check the vent’s condition. See if there is stuff you can easily pull out from the top with your hands or even a wire.

Next, go up with a garden hose and start pouring water down the vent stack. As the water accumulates inside the vent, its weight will unclog whatever is clogging it and be washed down the drain.

5. Call in the Professionals

When you have tried everything unsuccessfully, it is time to call a professional plumber. These guys have seen all manner of plumbing problems and will undoubtedly know what to do.

I would advise against opening the cleanout plug unless you have plumbing experience. The cleanout plug allows you to access your house’s drainage system.

If you remove the cleanout plug cap, there is a chance that all the sewage trapped inside the drainpipe will forcefully flow out. You will then have a bigger problem than the one you had in the beginning.


If your toilet bubbles when the bathtub drains, you should act quickly to prevent dealing with even more difficult and expensive repairs. You should also occasionally clean all your drainpipes to prevent clogs from happening in the same place.

Talk with all the family members, sensitizing them on what causes toilets to clog and what not to flush down a toilet. Occasionally pouring hot water down all the house drains effectively cleans the drains and, therefore, prevents clogs.