Why Does My Bathtub Gurgle When I Flush the Toilet?

Indoor plumbing has of course made life a lot easier and a whole lot more sanitary. But with that being said, plumbing systems do not come without their problems. One thing that you might notice is that when you go to flush the toilet, your bathtub ends up gurgling and sputtering.

Although those noises might seem very odd, there are some very common issues that may be causing these sounds, and some pretty easy fixes too, for the most part anyway.

Why Does My Bathtub Gurgle When I Flush the Toilet?

3 Reasons Why Bathtubs Gurgle When a Toilet Is Flushed

What you need to know here is that there are three main reasons or primary causes as to why your bathtub might make gurgling noises when the toilet is flushed.

1.  Air in the Drain

Bathtubs are usually always outfitted with air vents that control how much air flows through the pipes. These vents are extremely important in controlling both airflow and water flow. However, these vents can get closed, clogged, or be improperly built, which then causes air to be trapped within the piping system. The air that is trapped within the pipes will then cause the water to gurgle when the toilet is flushed.

2.  Air Coming Out of the Bathtub Drain

If your pipes happen to be clogged, especially if the drain leading from the bathtub is clogged, it can force air to come out through the drains. In other words, due to the lack of air and water flow through the pipes, when you go to flush the toilet, that pressure differential from the water rushing downwards will cause air to flow upwards and out through the drain, thus creating that gurgling noise. That gurgling sound may be caused by nothing more than a clogged or semi-clogged bathtub drain (or toilet drain) that is forcing air up through the drain when the toilet flushes.

3. Lack of a P-Trap

Yet another common cause of a bathtub gurgling when the toilet is flushed is if your bathtub does not have a P-trap. Most modern bathtubs are outfitted with these P-traps, and their purpose is to keep the drain pipe full with a specific amount of water, and also help to keep air out. Therefore, if your bathtub does not have a P-trap, when the toilet is flushed, air will be able to flow freely in the drains, thus creating that horrible gurgling noise.

P-Trap

How to Stop Your Bathtub from Gurgling When You Flush a Toilet

Now that we know exactly why your bathtub makes a gurgling noise when the toilet is flushed, let’s take a look at all of the possible solutions based on those issues that we discussed above. We will be starting with the simplest solutions, so let’s get right to it.

1.  Unclog Any Drains That Might Be Clogged

As mentioned above, if your drains are clogged, and yes, this could be either the bathtub or the toilet drain, when you go to flush the toilet, it can cause air to rush up out of the bathtub drain, thus creating that gurgling noise.

Therefore, the solution here is to get rid of any possible clogs that may be in the way. Refer to the points below for various options in terms of unclogging your drains. Start with the first one, as this is the simplest solution, and if that does not work, then move on to the next, and so on and so forth.

Solution #1: Plunger

Take some duct tape and cover the bathtub and sink drains, as this will prevent air from coming out when you plunge the toilet. If the obstruction is further down than where the bathtub pipe meets the toilet pipe, when you plunge, instead of getting rid of the clog, the air will just come out of the tub, so tape the tub drain shut. Give your toilet a couple of dozen good plunges and take the tape off the bathtub drain. Flush the toilet. If the gurgling persists, try plunging again, and if this does not work, move onto the next unclogging solution.

Plunging a Toilet

Solution #2: Drain Snake

Something else that you can try doing to remove clogs is to use a drain snake, aka a plumbing snake or toilet snake. Insert the plumbing snake into the toilet, and keep twisting until it goes as far as possible, or until you hit an obstacle. If you hit an obstacle, twist the snake back and forth and then pull it out (hopefully along with whatever was clogging the pipe). If this does not work, try doing the same thing for the tub drain as you just did for the toilet drain.

Other Solutions

The other thing that you can try doing is to use a chemical unclogger (make sure that it is toilet safe!). You can get two bottles, one for the toilet and another for the tub. I also wrote in more detail about unclogging here.

If none of the three above options worked (and you are sure that there is indeed a clog), you will need to call a plumber. However, if you are not sure that a clog is the cause of the problem, move onto the next solution on our list first.

2. Check the Bathtub Vents

If unclogging the drains has not provided any result then the next thing to do is to check the venting system of your bathtub. Venting systems are always located up on the roof, which means that leaves, dirt, and other obstacles can clog them. This means that these vents need to be continuously cleaned and kept dirt-free.

All you really need to do for this process is to go up onto the roof and see if the vent’s screen has any leaves or debris on it. If possible, remove the debris by hand. What you want to do now is to use a garden hose to force water down the vent pipe. If you see that the water is backing up, then there is a blockage. If this vent is blocked, you can use a drain snake to unclog it. Finally, if this does not work, you will most likely need to call a plumber or a ventilation expert.

3. Install a P-Trap

If your bathtub does not have one of these P-traps, you will need to install one in order to stop the gurgling from happening when you flush the toilet. Unfortunately, installing a P-trap is most likely something that you cannot do on your own and you will need to call a professional for assistance.

Should You Call the Plumber to Fix This Problem?

If the problem is as simple as unclogging the drain, then this is something you can do on your own. However, when it comes to checking the venting systems, especially in terms of going up on your roof, which can be a safety hazard, you may want to call a plumber.

When it comes down to it, plumbing systems can be a bit finicky, which means that if you do not know what you are doing, you are best off hiring a professional. Moreover, when it comes to installing a P-trap, this is something that you definitely won’t be able to do on your own.

Summary

There you have it, the most common cause and solutions to a gurgling bathtub when the toilet is flushed. Remember folks, when in doubt, it’s probably best to call in a plumber for assistance.