December 17, 2017

Why does my toilet bubble when I run the washer?

It’s not a disaster or even a serious problem really, but having your toilet bubble when you do the wash can be a curious thing. Calling a professional like the Plumbing Detectives, an experienced Sydney plumber service, may not be necessary. Find out why.

What Causes the Gurgling?

First of all, you need to understand what is going on in your plumbing. Behind the scenes, there are various levels of water and air in your pipes at all times. The whole system is under some amount of pressure as well, which changes through the day as taps are opened and the toilet is flushed. Vents are part of the system to allow air to move in and out, keeping the pressure balanced and everything running as it should.

When that pressure level is out of balance, your plumbing system can develop vacuums or pressure build-ups in unexpected places. In this particular case, that means the toilet. Air movement in the toilet drain causes the bubbling. If the air movement is strong enough, it can actually suck the water out of the toilet bowl, removing the “cap” that holds in the sewage gases that accumulate in the toilet drain. At this point, you have a more serious problem than just a few gurgles.

So this is the main root of the problem: unequal pressure in the pipes. There are two possible sources for this.


How your plumbing system is vented can be the source of your problem, though a potential blockage could be creating a temporary problem. When the toilet and the lines serving your washing machine are using the same vent, the sudden rush of water that comes with a washing machine draining will create a sizable vacuum in the system, which leads to the bubbles in the toilet. Common venting routes are not unusual even if they are not the best way to plan out your plumbing. You might want to talk to a plumber about adding extra vents or changing the pipe routes.


The other half of the system that can cause the gurgling is the drains. This is where a blockage is more likely going to be the root cause, especially if the system was running bubble-free before. Examine the drains and make sure they are clear before doing anything else. If that doesn’t fix your gurgling, then there is a more fundamental problem with the pipe routes again. Sharing drains will cause pressure disruptions during the wash drain cycle that appear in your toilet bowl.


A little bubbling now and then isn’t going to be a disaster and shouldn’t be a cause for alarm. It’s not a great situation but you should keep an eye on it. As mentioned earlier, drastic pressure changes when the washing machine drains can be enough to pull all the water out of the bowl. This is a more serious concern. That water is there for a reason, to create a fluid and flexible lid on an otherwise open pipe. Gases from inside the drain are hazardous and should not be allowed to go venting into your bathroom. If this starts to be a regular occurrence, call the plumber.

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