How to Vent a Washing Machine Drain Pipe: 6 Step Guide

If you’re installing a washing machine for the first time, you’ll have to install a drain. Under international plumbing code, that also means installing a vent. Luckily, adding a vent to a washing machine drain is relatively easy, especially if you’re venting from the bathroom. 

However, the process of venting a washing machine drain pipe will vary depending on the room you’re installing the machine in. If you’re in the bathroom, you can connect the drain vent to the shower vent. If you’re in the attic or the basement, you might want to run the drain directly outside. 

How to Vent a Washing Machine Drain

Washing machine drain vents allow gas and air out of the drainpipe. Air bubbles collect over time and can result from either air in the water or rising sewage gases. Both will cause difficulty draining your washing machine and could cause bad smells in your bathroom. In the case of sewage gasses, they could even be a fire hazard when your washing machine is on. Luckily, learning how to vent a washing machine drain pipe is relatively easy. 

In most cases, you’ll be installing the washing machine in the bathroom. This means you can connect the washing machine drain vent to the toilet and sink vents. 

In addition, if you haven’t opened up your wall, you’ll want to do so. That will mean removing any drywall in the way of either your existing vent branch or your external vent location. 

Things you’ll need: 

  • 2” PVC pipe (Measure the distance between the drain and the branch vent or the external vent to get the length.) 
  • 2” PVC elbows and bends as necessary to reach the vent 
  • A 4” to 2” PVC T or angle connection 
  • A 2” PVC T + a second T or corner depending on if you’re installing a new branch vent or cutting into an old one 
  • If you’re installing an external vent, a vent cap, and silicone suitable for external use 
  • A power drill 
  • Forstner or spade bits 21/8th inch or 2/14 inch 
  • A hacksaw (small and able to fit into tight spaces) 
  • Pipe cement 
  • Tape measure 
  • A leveling line or a string, nails, and chalk 
  • Safety glasses 
  • A level or angle finder 
  • Disposable gloves 
  • 2×4’s to reinforce the wall studs
  • Wood screws 

1. Measure your vent pipe 

Decide where you’re venting your washing machine. Under international plumbing code, you can vent outside, to the vent stack, or to a branch vent. Normally the location that makes sense depends on where you’re installing the washing machine. 

  • Kitchen or Pantry – Connect to the kitchen vent branch or go directly outside
  • Bathroom – Connect to the bathroom vent branch or go directly outside
  • Under stairs or in attic – Connect to the vent stack or go directly outside
  • Basement – Connect to the vent stack or vent directly outside

The most important thing is understanding where you already have vent pipes. If you can connect to an existing vent pipe, it’s always better than drilling a new hole in the exterior of your home. However, that might not be possible if your vent pipes are far away. 

The vent pipe must be at a minimum of a 45-degree angle to prevent condensation and water buildup.  Your pipe may also be horizontal. From there, you can measure the distance to see how much pipe you need by measuring directly to the location you want to connect to.  

2. Connecting the vent to the drain 

The vent can install between 4 inches from the weir on the trap and no more than 8 feet from the trap. Closer is normally better, so most people choose to connect within a foot of the weir, which is the point at the bottom of the trap where it connects to the U bend. 

To install the vent, cut the pipe and install the 4” to 2” connection. You’ll want to wait to glue it until you’ve installed the full length of pipe, so you have some freedom to move things around. 

3. Drill out the vent pipe

Take your pipe and figure out how you want it to go through the wall. Best case scenario, you can run it straight up, between joists, without drilling in them. However, it’s much more likely you’ll have to drill a passageway from the entry point of the pipe and at an angle through the joists and studs to get the vent where it needs to be. Here, it’s important to note that if the hole takes up more than 25% of the width of the stud, you’ll want to add a reinforcement. 

Here, most people prefer to use a string or a chalk line to trace the line between the vent location and the pipe’s start. You can use an angle finder or a level to ensure you have at least a 45-degree angle. 

Drill through the studs at the angle you’d like the pipe to be using a Forstner bit. The bit should be slightly larger than the pipe. If you have 2×4 joists, you’ll want to reinforce the wall by doubling up the studs first. 

4. Run your vent pipe 

Measure and cut your vent pipe sections with a hacksaw. Lay them out with the connection pieces. Slide everything into place and make sure it fits well. 

5. Connect to the vent 

Whether you’re connecting to an exterior vent or to the branch pipe, you can do so by installing a connection between the last PVC pipe and the branch or vent. This normally means using a T or a corner to connect the pieces. 

Exterior Vent – Directly connect the PVC to the vent and use glue to secure it in place. You can install an exterior vent by drilling through the wall, installing a vent cap, and using exterior silicone to seal the vent. Learn how to choose your exterior vent here

Branch Vent – Cut the vertical pipe and use an angled T-fitting to connect it. Your branch vent is probably also 2”. However, you should pay attention and make sure you get the appropriate size. Use glue to secure this. 

Once you’ve connected to the vent, you can go over the pipes and glue them. Make sure the space is well ventilated. You’ll also want to use gloves to protect your hands. 

6. Install a Studor Vent

Install an air admittance valve on the washing machine to ensure that your machine admits enough air to prevent air bubbles in case the shower or sink is on at the same time as the washing machine. AAVs or Air Admittance Valves are negative pressure one-way valves that simply allow air to pass through, eliminating or reducing the need for the standard drainage system. 

Is Venting a Washing Machine Drain Mandatory?

Any trapped rain is required to have a vent under ICC code. This means that you’ll have to connect your washing machine to the vents. However, not all city building code requires that you have a vent. On the other hand, it’s always a good idea to install a vent, simply because it reduces the chances of overflow and flooding your bathroom. 

Washing Machine Drain Vent Requirements 

Drain vents are regulated under international building law. Poorly installed plumbing can be dangerous because it can result in flooding, fire hazards, and buildup of toxic gasses. Therefore, it’s important to check local regulations and follow them when installing a vent. You may not be allowed to legally vent your drains yourself. Therefore, it’s always important to check local plumbing codes before proceeding. 

  • Washing machine vent pipe size is 2”. You may also use 4” however this is unnecessary. 
  • Washing machine vents should be connected a minimum of 4” from the trap weir.
  • Horizontal branch vents must be at least 5” above the floor level rim of the highest trap being vented. 
  • External vents must be at least 9” off the ground.
  • Common vents may go directly outside.


Installing a washing machine vent is relatively simple. However, chances are, you still have questions. 

Can I use a Studor vent for a washing machine drain?

Yes, you can. You should also use a Studor vent if you’re connecting a washing machine to a branch vent. In most cases, a mini vent is suitable for a washing machine, however, it may not prevent sewage smells if gas builds up. Therefore, you normally want the classic drain pipe vent as well. However, you should not use a Studor vent when the vent branch is also connected to the toilet unless you have an AAV designed for the purpose.  

How far should a vent be from the washing machine drain?

The washing machine drain should be a minimum of 4 inches from the trap weir and a maximum of 8 feet. 

Can I put the washing machine, shower, and the toilet on the same vent? 

Yes. You can add up to three vents on a single, communal branch vent. However, you shouldn’t always use Studor vents when connecting to the toilet, as this can vent methane into your bathroom. Instead, it’s better to connect the sink, shower, and washing machine to a single line. You can then vent the toilet separately. 


Installing a washing machine vent is a relatively simple job. However, if you don’t want to take apart your wall, you may be able to get away with installing a Studor vent. On the other hand, you can normally easily connect your washing machine vent pipe to the existing vent stack – to very quickly and properly vent your washing machine. 

Here, it’s important to check local regulation. Some cities allow you to install a washing machine with just a studor vent. Others require that you use external ventilation for any vent connected to the sewage. Therefore, requirements will vary by area. 

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