Can a Washer and Toilet Share the Same Drain?

In some cases, you can drain a washing machine into an existing toilet drain. However, you should never add a toilet to an existing washing machine drain. This is because washing machine drain lines have a smaller diameter than toilet drains. Connecting a toilet to a washer drain will cause a sewage clog.

Additionally, there are special considerations when plumbing your washing machine and toilet to the same drain pipe if your home has a septic system. Above all, work with a professional plumber to make sure your planned installation is up to code.

Can a washer and toilet share the same drain?

When Can a Washing Machine Share a Drain with a Toilet?

Plumbing your home correctly is essential to prevent clogs and leaks. You can have your washing machine and toilet share the same drain when ALL of the following are true:

You are Adding a Washing Machine to an Existing Toilet Drain

You can only drain a washing machine and toilet to the same place if the washing machine will drain to an existing toilet drain. Toilet drain pipes are typically 3 inches in diameter. This is larger than the minimum diameter required for a washing machine drain. So, the toilet drain will be large enough to handle the water that drains from the washer.

You Do Not Have a Septic System

If your home is linked to a municipal sewer system and you DO NOT have a septic system or septic tank on your property, you can drain your washing machine to the toilet drain line. Your city’s sewer system is designed to handle the wastewater from both your toilet and washing machine safely.

You Install a Proper P-Trap

When plumbing any washing machine it is essential to install your washing machine P-trap at the correct height. This is even more essential when you are adding a washing machine to a toilet drain. A P-trap at the incorrect height allows wastewater to backflow back into the washing machine. When your toilet and washer share the same drain, backflow caused by a poorly installed P-trap will allow raw sewage to flow into your washing machine drum.

Your Installation Will Meet Plumbing Code

Drain pipe size and P-trap height are only part of the equation when it comes to properly installing washing machine waste pipes. In order to be certain your installation conforms with plumbing code, it is best to work with a professional plumber. They can help you determine a safe and effective installation for your home.

When Should a Washing Machine Not Share a Drain with a Toilet?

It is essential to rule out any potential dangers of draining a washing machine and toilet to the same drain. If ANY of the following are true, DO NOT attempt to combine the drain lines for these two appliances.

You are Adding a Toilet to an Existing Washing Machine Drain

Never add a toilet to a washing machine drain line. Plumbing code for washing machine drains specifies a pipe diameter of 2 inches. This diameter is much too small for a toilet, which requires a 3-inch-diameter drain. Draining a toilet to a washing machine drain will cause clogs that will render both your toilet and washer unusable until the system is re-plumbed.

Even worse, some homes have greywater systems that disperse used washing machine water into the soil. It is illegal, unsanitary, and hazardous to drain a toilet in this manner. Doing so will release raw sewage onto your property, which creates a health risk. So, you should never add a toilet to a previously installed washer waste pipe.

You Have a Septic System

If your house has a septic system, the toilet must drain to the septic tank. However, your washing machine should not drain to your septic tank. This is because draining washing machine water to your septic tank can cause clogs or flood the system and cause premature release of waste matter to the drainage field. Instead of draining your washing machine to your septic tank, consider these washing machine drainage options.

Your Installation Does Not Meet Plumbing Code

As stated above, it is essential to work with a licensed plumber to be certain your planned installation meets UPC (universal plumbing code). If you are told that your plans are not up to code, do not proceed with the installation. It is essential to make sure that everything from the drain line to the vent pipes meet code. Otherwise, you risk serious damage to your home and plumbing system.

Where Does the Water From Your Washing Machine Drain?

Your home washing machine either drains to the sewer line or to a separate greywater dispersal system. If your home is linked to a sewer system and you DO NOT have a septic tank, then your washing machine most likely drains to the sewer line. If your home DOES have a septic tank, then your washing machine probably drains to a separate greywater system that allows used washing machine water to filter back into the soil.

  • Your washing machine may drain to the sewer line or to a separate greywater system.
  • If your home is linked to a sewer system, then your washing machine is extremely likely to drain to the sewer.
  • If your home has a septic system, it is common for washing machine water to be filtered back into the soil via a dedicated greywater system.
  • If you are unsure of your home’s drainage system, follow our guide to determining if your washing machine drains to the sewer.

It is 100% necessary for your toilet to drain to a sewer line that runs to a municipal sewer system or a septic tank. This is because toilet wastewater is considered “blackwater,” which must be contained and handled through sanitary processes. However, washing machine water is “greywater” which is not fresh water. So, it can be treated as waste water, or dispersed belowground to return water to the soil.

Can a Toilet and a Washing Machine Share the Same Drain?

If you are considering combining your toilet drain with a washing machine drain, remember these key facts:

Requirements to Combine Washing Machine and Toilet Drain

  • You are adding a washing machine to an existing toilet drain, not vice-versa.
  • Your home does not have a septic system.
  • You will install the P-trap at the correct height to prevent backflow.
  • The entire installation meets plumbing code.

Dealbreakers that Prevent Combining Your Washing Machine and Toilet Drain

  • You are attempting to drain a toilet to an existing washing machine drain.
  • Your home does have a septic system.
  • The installation does not meet plumbing code.

These quick facts will help you decide whether or not the installation is possible before you go further. This can save you headaches (and plumbing clogs) down the line.

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