In many households, the washing machine and the kitchen sink are set up to share a drain, especially if the washing machine is set up anywhere near the kitchen. It’s also possible that both the sink and the machine empty into the same toilet waste pipe.
Plumbers describe the oversized configuration of pipes so that air can pass through a waste line while water is flowing as ‘wet venting’. A problem can easily arise in these pipes if a slight blockage develops because this would mean a restriction in airflow, thus the slowing of the flow of water.
This means that if the washing machine is running a cycle at the same time that the sink has a backup, the blockage may be stopping water from running properly through the line.
This may lead to water being rerouted from the sink’s pipes all the way through into your washing machine during the cycle. A highly unpleasant situation may arise when you open the machine door expecting clean clothes and discover only dirty sink water.
If this is an issue that you have noticed happening in your machine, it is best to get it fixed as quickly as you can. It should ideally be an easy fix but could worsen if left for too long.
How to Stop Water from the Sink Going into the Washing Machine
1. Try plunging the sink
The blockage should be resolvable by plunging the sink while the backup is happening. It would be a good idea to simultaneously cap off the drain of the washing machine and cover the sink’s overflow holes while plunging.
It’s advisable to also plunge any nearby toilets in case the blockage is further along the pipes. There are various online tutorials and videos on how to unblock a sink, but a plumber should be able to help you with the issue if you are uncertain about how to do it yourself.
2. Check the dry vents
If you’ve tried plunging the sink and the toilet and are seeing no visible difference, then the problem could be the dry vents. These are the vents that connect from the sink and washing machine to the main vent stack.
If both your sink and washing machine have their own vents, then the problem could be a blockage in the main stack.
You can try plunging the drains that connect to these, but if that fails then it’s likely that the roof opening is being blocked by sticks or leaves. Try removing this blockage in order to clear the vents.
Alternatively, many newer washing machines are installed with vents called Studor Air Admittance Valves, which do not require the running of new vent pipes through the walls.
These are designed so that negative pressure can open a spring-loaded valve and let air in to keep the water flowing. However, they can sometimes stick. Luckily, they are relatively easy and affordable to replace and can be simply screwed in and out.
3. Check that the washing machine is installed properly
The last possible reason for sink water to be running into your washing machine is if the washing machine has not been correctly installed. It’s likely that if the washing machine drain hose is connected to your kitchen sink when the sink is emptied, a bit of the water from the sink ends up to your washing machine through the drain hose connection.
Your trusty plumber should be able to figure out exactly what it is that is causing your sink and washing machine to give you problems, and with any luck, they will be able to fix it in a jiffy.
An adventurous book lover with an animal obsession and a proclivity for travel and spontaneity. Used to passionately despise cleaning but has grown to enjoy it thanks to learning all the best tricks and shortcuts to guaranteeing a stress-free routine and a spotless home.