What Are Washing Machine Drain Hose Backflow Prevention Options?

Washing machines drain their wastewater into either a laundry tub, outside pipe connection, or standpipe.

Regardless of the method you use for draining your washing machine’s wastewater, it’s important to work to prevent backflow from occurring.

You can ensure optimal performance and prevent backflow by making sure your drainage is properly installed. By following some key steps, you can effectively prevent backflow and ensure that potential damage doesn’t occur.

What Are Your Backflow Prevention Options?

Optimal Standpipe Height

What is it: A standpipe connects your washing machine’s drain pipe to your home’s waste stack. By choosing to use a standpipe instead of connecting your washing machine to a drain line, you can avoid water overflow, as well as unwanted fumes from the sewer.

This is a sturdy vertical pipe that has a curved end. This end is designed to hold water so that the smell of sewer doesn’t permeate your laundry room and home.

The standpipe also serves to ensure that the water level in the washing machine’s tub doesn’t rise above the drain. All standpipes should be no less than 36 inches from the top of the washing machine.

This helps to prevent siphoning from occurring while keeping wastewater from backing up into your washing machine.

If backflow does occur, the siphoning can result in not only the water coming back into your washing machine but also out into the floor of your laundry room.

This can lead to serious damage to your home. If your laundry room is located with floors below it, you could be looking at a major headache and a lot of clean-up.

Why it fails: When backflow occurs in your standpipe, it’s usually one of two things. It could be due to a clog between the drain pipe and waste stack or blockage in the main sewer pipe.

Obviously, you would rather have a clog between the drain pipe and waste stack. One is a relatively easy fix while the other can lead to exponential expenses.

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If the issue is with an improper height, you could be seeing backflow issues and overflowing wastewater on your laundry room floor.

If the standpipe is too low, overflow can occur, causing water to come back out of the standpipe. If the standpipe is too high, your washing machine will have to work harder than usual to keep itself drained. When this happens, wastewater can return to the washing machine.

How to fix: If the clog is in the drain hose that connects to the back of your washing machine and rests in the standpipe, begin by removing the drain hose.

If you have an air compressor, shoot some air through the drain hose after it is removed. If the airflow is weak, you’ll know that there’s an obstruction blocking your water flow.

You can use a handheld drain auger to snake through the drain hose and break free from the congestion. Alternatively, you may use a stout piece of wire to fish through and attempt to knock loose and buildup.

Once the drain hose is free of blockage, you may reattach it to the back of the washing machine and rest the curved elbow back into the standpipe.

If No Clog Is Present

If there wasn’t a clog in the drain hose, you’ll need to move on to the standpipe. After taking the drain pipe out of the standpipe, you will need to use a handheld drain auger or something similar to fish for any blockage.

Worse case, you may need to disconnect your standpipe and trap to ensure that they are both clear and able to drain water sufficiently.

If neither are clogged, the sewer may, unfortunately, be the issue. At this juncture, it’s best to contact your city to see if the problem is on their end (and also, their dime).

If the problem lies with you, a licensed plumber will need to come out and inspect your plumbing. From there, they can give you an estimate as to how much you’ll be looking at to resolve your problem.

If the issue is with the height of your standpipe, adjust the height to within proper parameters to ensure optimal water flow.

Drain Hose

What is it: Your washing machine’s drain hose is responsible for carrying wastewater from the unit to the standpipe, laundry tub, or outside pipe connection.

The drain hose connects from the back of the washing machine and rests via a curved elbow into a laundry tub or standpipe (a standpipe is also part of an outside pipe connection).

Why it fails: There are a few reasons why your drain hose could fail. Knots and kinks can result in poor water flow, resulting in backflow and flooding in your laundry room. Clogging is also a possibility that can lead to backflow.

Conversely, a damaged drain hose can cause you to see backflow and possible flooding issues in your washing machine or the laundry room.

How to fix: Practicing proper maintenance and regular cleaning will help to ensure that your drain hose remains free of excess fibers and debris.

You should make sure that your drain hose isn’t being pushed against by other appliances or objects. Any pressure against it can result in irregular water flow and lead to backflow.

If you discover that your drain hose has become damaged in any way, it’s best to replace it right away so that you can avoid other potential issues.

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Clogs & Stops

What is it: Every time your washing machine sends its wastewater through the drain hose and into your drainage option, it is sending more than just water. This is what leads to potential clogging and other issues.

Why it fails: As it is called wastewater, there are also traces of fibers, dirt, and other debris that build up over time.

If too much of this accumulation is allowed to collect in your drainage, it can result in a clog that causes backflow.

The clog usually occurs within the drain hose or standpipe. As such, it’s important to practice regular cleaning.

How to fix: Making sure that you regularly clean your drain hose and everything that comes after it will go a long way in preventing clogs and potential backflow.

If backflow does occur due to a clog, it’s important that you never use chemicals to try to break loose the clog. These can come back through your washing machine and permanently damage it, not to mention what it will do to your clothes.

If you need help tackling a clog, refer back to “Optimal Standpipe Height” and read the “How to Fix” section.

There, you will learn what you need to do to check your drainage and how you can remove and clogging that may have accumulated.


Knowing how to handle clogs will make a big difference in preventing backflow. Your drain hose is the first piece of equipment that sees all of the wastewater from your washing machine.

By working to keep it clean, you can prevent potential clogging in the plumbing that comes after the drain hose. Make a habit of taking the time to regularly clean your drain hose and you will be less likely to experience backflow.

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