If you’ve ever been in the unfortunate situation of having a toilet that bubbles when the bathtub drains, you know how frustrating it can be.
This is a common plumbing problem that many people experience, but most don’t know how to fix.
In this article, I will walk you through the steps of fixing a bubbling toilet so that you can get your plumbing back to normal!
Reasons Why Toilet Bubbles When You Drain the Bathtub
There can be a lot of reasons behind the issue, so it can be a bit intuitive to figure things out.
Partial Clogs in the Drain Line
The majority of the time, a partial clog in your sewer line is the reason for your toilet bubbling when you empty the bathtub.
When there is a partial clog, it causes a back-up of water in the pipes, which then forces air into your toilet bowl through the P-trap.
While partial clogs are usually not a big deal, if it happens frequently, it could be a sign of a bigger problem.
To know if you have a partial clog, try flushing your toilet after using the bathtub. If the water in the bowl rises and then goes down slowly, you probably have a partial clog.
Sewer Gas Not Escaping through the Proper Channel
Another reason why your toilet might bubble when you drain the bathtub is because of sewer gas.
Sewer gas is made up of various gases, including methane, hydrogen sulfide, ammonia, and more. It is produced when sewage decomposes, and it can build up in your pipes if there is nowhere for it to escape.
There are a few potential causes of this problem, but the most likely one is that your P-trap is dry. The P-trap is the U-shaped pipe that connects your toilet to the drain.
It’s located under your toilet bowl.
The P-trap is filled with water, and this water forms a seal that prevents sewer gas from coming up through the drain.
If the P-trap dries out, that seal is broken, and sewer gas can escape through that opening instead of the vent.
Here’s how to find out If sewer gas might be the cause of your toilet bubbling:
First, try to identify if there’s an odor in your bathroom. If there is, and it smells like sulfur or eggs, then it is probably sewer gas.
And if it is coming from your toilet, then it is most likely because there is a build-up of sewer gas in your pipes.
To further verify, light a match and hold it near the toilet bowl. If you hear a hissing noise or see the match flame being drawn towards the toilet, know that sewer gas is most likely the cause of your problem.
Air Vent is Blocked or Damaged
The air vent on your roof is responsible for allowing fresh air into the sewer line. If the air vent is blocked, this can cause pressure to build up in the sewer line.
Subsequently, this pressure can cause water to back up and create bubbles in the toilet.
Finding out if it’s an air vent issue is quite easy. Simply go outside and see if the air vent on your roof is clear. If it’s not, then you know that this is most likely the cause of your problem.
Septic Tank is Full, Damaged, or Have Other Issues
If you have a septic tank, it’s important to have it pumped regularly because solids can build up and cause a blockage. This blockage can cause water to back up and create bubbles in your toilet.
Diagnosing whether you have a septic tank issue on your hands is quite easy. The root of the issue is probably your septic tank if it hasn’t been pumped in a while.
Usually, you need to pump the tank every 3 to 5 years depending on how many people reside in the house and the tank size.
Wrong Trap Size
One final possible reason for toilet bubbling is that the trap might be the wrong size.
The trap is simply a curved portion of pipe that holds water, creating a barrier between your home and the sewer.
If the trap is too small, it won’t be able to hold enough water to create an effective barrier. This can cause sewer gases to escape and bubble up in your toilet.
To know if a wrong trap size is the cause of your toilet bubbles when you drain the bathtub, simply look at the water level in the toilet bowl. If it goes down significantly when you drain the tub, there is a good chance that the trap is too small.
How to Fix a Toilet that Bubbles When Bathtub Drains?
Now that you know the reason why it’s happening, let’s fix it without any further ado.
Fixing Partial Clogs:
- Put on a pair of rubber gloves and remove any visible debris from the drain. Debris may include hair, soap scum, or small pieces of food.
- Then pour a half-cup of baking soda down your toilet bowl.
- Follow that with a half-cup of vinegar.
- Let the mixture sit for 15 minutes before flushing.
- Next, use a plunger to try to dislodge the clog. If that doesn’t work, you may need to snake your toilet’s vent line.
To snake your toilet vent line, follow these steps: You will need to get a plumber snake tool.
- Flush the toilet to empty the water.
- Insert the plumber snake into the toilet. Feed until you reach resistance.
- Now, twist it so that the clogging material gets hooked up by the toilet snake. Do some forward and backward movement while twisting to dislodge any clog.
- Finally, flush one last time.
If done correctly, this should clear away any partial clogs and eliminate any more toilet bubbling when you run your bathtub drain.
However, If these steps didn’t work, or if you’re not comfortable doing them yourself, call a professional plumber.
They will have the equipment and experience necessary to quickly clear the clog and get your toilet back to working properly.
Fixing the Sewage Gas Escaping through the Toilet
While this happens only when there is no adequate escape for the sewer gases, you need to remove all the blockages from the vent pipe first before moving forward.
- All drains should be properly vented so that sewer gas can escape through normally.
- Check to see if the toilet bowl has the water up to the regular point. If it is, nothing to worry about. Flush and hope that the issue gets fixed after removing the vent pipe blockages.
Note that it is important to have the toilet inspected by a plumber to ensure that there are no leaks or other issues that could be causing the problem.
Fixing Air Vent Issues
To fix this, you will need to clear the blockage in the vent. You can do this yourself by using a ladder to climb up to the vent and remove whatever is blocking it.
An easy way to prevent air vent issues is to ensure that no trees or shrubs are growing near the vent.
If there are, trim them back so that they are at least two feet away from the vent. This will assist in preventing leaves or branches from blocking the air vent.
Fixing Septic Tank Problems
Have the septic tank pumped and inspected. If there is too much waste in the tank, it is bound to make issues for your home.
In addition, the leach field should be checked for blockages or leaks. If any of these problems are found, they should be repaired/treated as soon as possible to prevent further damage to the septic system.
As a rule of thumb, have the tank pumped out every three to five years. This will remove any sludge that has built up over time.
Replace the Wrong P-Trap with the Correct Size
This is a very rare phenomenon and is extremely difficult for a homeowner to attempt doing this.
First, modern toilets don’t need any additional p-trap. The toilet bowl itself has the p-trap built into it. So, you don’t need to worry about it.
If you have a very old house that utilizes a PVC p-trap with the toilet, there is hardly any chance that the p-trap will be of incorrect size. Since the pipe needs to be fitted with the toilet plunge, the plumber can’t just take and use a small p-trap.
However, on some rare occasions, it happens that the p-trap of the correct size cause issues due to their manufacturing defect.
I recommend calling a professional plumber in case the other solutions didn’t have any positive impact on the issue.
To Summarize
If your toilet bubbles when you run water through the bathtub drain, it is most likely due to a clog somewhere in the plumbing line.
You need to figure out where that clog is and resolve the issue.