Why Your Toilet Bubbles When Washer Drains

A common question that people ask is why do toilets bubble when the washing machine drains? Here’s the science behind it:

If your toilet gurgles or bubbles when the washer drains, it’s mostly because your drains are partially or completely clogged. Commonly, washing machines and toilet drains are connected with each other. When the washing machine drains are clogged, it forces air and water to go back through the toilet drain and bubble.

So what can you do to prevent it?

In this article, I’ll explain the causes of toilet gurgling when the washer drains and how you can prevent this situation from happening again.

Read more to find out.

5 Reasons Why Your Toilet Bubbles When the Washer Drains

clogged toilet drain
Image from Sugar Plumbing

#1 Partial or Complete Clogs

The most common reason for toilet bubbling when the washer drains is that your drains are partially or completely clogged. When your drains are partially clogged, there’s no way water can pass down the drains easily. This results in water coming out through another opening, i.e., the toilet bowl.

This phenomenon is called backflow in fluid mechanics.

The situation will worsen if you don’t take any measures to unclog drains as the flow of water will keep reducing with time.

#2 Blocked Vents

Blocked vents create negative pressure in the drains, pulling air from wherever it can, and creating a gurgling sound. This happens because the water flowing through the pipes forms an airtight seal that pushes the air in front, resulting in a vacuum.

Most vent pipes don’t have any cover, due to which animals, pests, and dirt go into the vent pipes.

This is one of the worst scenarios to happen to you when the washing machine drains.

Blocked vents can result in pulling the water out of the toilet bowl. The sewer gases will escape out of it and cause a bad odor in the bathroom.

It won’t be a big problem if you’re using a laundry sink to wash clothes instead of a washing machine as a washer creates high pressure with the sudden release of water.

#3 Blocked Sewer Line

If you see multiple fixtures gurgling in your house, i.e., bathtub, kitchen sink, etc. while the washer drains, it’s probably because your sewer line is blocked. The main sewer line carries out the water of the washer, toilet, sink, and every other appliance of your house.

If you see bubbles, it indicates that air is trapped inside the drainage sewer line. This leads to water, waste, or sewer gases overflowing from the toilet because there’s no way for them to leave your house.

Unfortunately, you can’t do much instead of changing the sewer line of your house with the help of a plumber.

#4 Connected Drains

Most washer drains and toilet drains are connected. The washing machine during the drainage creates high pressure in the drainpipe which overflows the toilet. If your washing machine is placed between the toilet and sewer stack, there’s a high chance that the toilet will overflow when the washer drains.

The fixture and toilet vent jointly in these situations. Through the toilet drain, the fixture may be vented as well. This is known as wet venting by plumbers.

You might also want to notice the length of pipe connecting the toilet and the washer with the drain pipe. Using a long pipe can fix the bubbling problem to some extent.

washing machine in the toilet

#5 Improper Washing Machine

Another reason for the toilet gurgling when the washer drains is improper installation of the washing machine. Improper installation causes poor water flow and more pressure in the drainpipe than it can handle, causing bubbles in the toilet.

If the installation was not done by a professional plumber, it might cause disturbance in the long run.

However, a washer installed correctly can still cause bubbles in your toilet. Since each washing machine is of a different size, area, and power, it might not be suitable for your laundry.

How to Stop Toilet Bubbling When the Washer Drains

Here are some tips on how to prevent the toilet from bubbling when you are in the middle of a load of laundry:

woman plunging the toilet

#1 Plunge the Toilet

There might be a clog close to the toilet surface and it’s easy to eliminate it with plunging. Use these steps to plunge your toilet properly:

  1. Place the plunger on the toilet.
  2. Press with light pressure.
  3. Start exerting more force.
  4. Keep plunging in and out for more than 20 seconds.

Do not break the plunger’s seal while exerting pressure to avoid extra mess.

#2 Clean Your Main Sewer Line

Blocked and clogged sewer lines have a role to play when it comes to toilet gurgling. Use hydro jetting to remove sewer line clogs. It’s the most convenient method to clean the sewer line and only requires toilet removal.

Any professional plumbing service would offer hydro jetting for your toilet.

roof vent stack

#3 Clean Your Roof Vent Stack

If there’s no cover on your roof vent stack, it will collect debris and block the air inside. Here’s how you can clean the roof vent stack yourself:

  1. Climb up the roof with a ladder.
  2. Locate your roof vent stack pipe.
  3. Take out the debris by hand.
  4. Pour water down the vent with a hose to push the clogs.
  5. Use a sewer snake if the clogs remain.

#4 Use Detergent With Fewer Bubbles

To inhibit bubbles, use commercial or castile soap instead of generic bar soaps which have detergents and chemicals added.

Keep your drains free of hair, sediment, and soap scum.

#5 Use Cold Water

Use cold water from the washing machine to clean your toilet and let it sit for a few minutes before flushing after use. This prevents bubbles because hot water would evaporate faster under high pressure, leading to air pockets in the bowl or pipe wall if too much force is applied.


Waste and water overflowing out of the toilet can be really messy. Make sure your toilet whirlpools silently without any gurgling noise or bubbles when using the washing machine.

Does your toilet gurgles too when the washer drains?

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