Toilet Leaks at Base When Washer Drains: Why & How to Fix?

Is your toilet leaking at the base when the washing machine drains? If so, you’re not alone. This is a common problem that can be fixed relatively easily.

In this post, we’ll explain why this happens and how to fix it. Stay tuned for our tutorial on how to do it!

toilet leaking at base when washer drains

Why Does Toilet Leak at Base When Washer Drains?

Does your toilet leak at the base when the washer drains? Here are the likely reasons why your toilet leaks and how to fix it:

You Have A Wet Vent Plumbing System

The main reason why your toilet is affected when washer drains is that they are connected. Your toilet’s drainpipe and washer’s drainpipe are connected through the wet vent plumbing system.

A wet vent is a plumbing system where the drainpipes of almost all the plumbing fixtures in the home are connected to a common main drain line. The main drain line conveys wastewater from various plumbing fixtures to the sewer. The main drain line is usually connected to the roof vent pipe, which allows the inflow of air and escape of gasses.

When your washer drains, it releases a lot of water into the main drain line. As the water rushes through the drain line, it pushes the air ahead of it out through the vent pipe. This is the normal process.

However, if there is a problem, the air will be trapped and forced to look for a place to escape. The two most common problems are blocked main drainpipe and blocked roof vent.

Either of these problems will cause your toilet to bubble or overflow when the washer drains. If you don’t attend to these issues as soon as possible, they may subsequently cause your toilet to leak at its base.

Partially or Completely Blocked Main Drainpipe

One of the reasons why your toilet may leak at the base is because the main drainpipe is partially or completely blocked.

When your washer drains into a blocked drainpipe, the flow of wastewater is restricted. As a result, the wastewater, as well as the trapped air, is forced back into the drainpipe. Both the wastewater and air will look for a place to escape and, in this case, your toilet.

As wastewater and air escape into your toilet, it will cause the water in the toilet bowl to bubble or overflow. Since the wastewater and air are moving at high pressure, you need to fix this issue as soon as possible. Otherwise, the high pressure may cause damage to your toilet’s wax ring, causing your toilet to leak at the base.


The problem is with the main drainpipe and not the toilet’s drain line, which can be easily accessed. Therefore, a plumbing auger (snake) may not be a suitable tool to fix this problem.

A better solution is to use a hydro-jet. A hydro-jet shoots up to about 4000 PSI of water into the main drainpipe. This is powerful enough to push off clogs in the main drainpipe. You only need access to the inside of the main drainpipe to achieve a positive result.

In case you can’t lay your hand on a hydro-jet or can’t access the inside of the main drainpipe, consult a professional to fix the clogged main drainpipe for you.

Blocked Roof Vent Stack

Another reason why your toilet may leak at the base is because of a blocked roof vent stack. A roof vent stack is a vertical pipe connected to your main drainpipe. Its function is to convey air and gasses through your main drainpipe without disrupting the flow of wastewater.

If the roof vent stack is blocked, there won’t be an entry of sufficient air to enable the wastewater from the washer to drain smoothly. As the wastewater tries to go down the drainpipe, it’ll draw air from the toilet drainpipe, causing the water in the bowl to bubble. If the wax ring is weak, the pressure may cause some of the water in the bowl to leak through the base.

Sometimes, the movement of the wastewater from the washer may cause gasses to escape from the roof vent stack. If the roof vent stack is clogged, the gasses, taking some wastewater with them, may be forced to leave through the toilet drain. This can also cause your toilet to bubble or leak at the base.


Fixing a blocked roof vent stack is easier. Simply climb to your rooftop and check inside the roof vent stack. If it doesn’t have a screen, dirt or debris might have fallen into your roof vent stack to clog it.

Clear off any dirt and debris, such as a nest, leaves, and so on, from the vent openings. If you can’t notice any blockage, you may use a flashlight to look into the vent or spray some water into the vent to detect clogs. If there are clogs inside the vent pipe, take them out using a plumbing auger.

If the plumbing auger can’t reach the clog, spray more water down the vent stack to dislodge the clog.

Fixing Your Toilet That Leaks at Its Base When Washer Drains

As I said earlier, if you don’t attend to the issue of toilet bubbles when the washer drains immediately, your toilet may begin to leak at the base.

However, if your toilet is already leaking at the base when your washer drains, don’t panic. Here is how to fix the issue (but make sure that you’ve first applied the two solutions above):

Step 1: Shut water supply to the tank by turning the water valve completely clockwise. Flush the toilet to empty the tank. After that, use a toilet plunger to empty the toilet bowl.

Step 2: Disconnect the water supply hose from the fill valve assembly on the toilet tank by turning the locknut anticlockwise. Don’t forget to place a bowl under the hose as you disconnect it to prevent water from spilling on the toilet floor.

Step 3: Remove the lid from the toilet tank. If there is still some water in the toilet tank, take it out using a sponge/foam.

Step 4: If your toilet is a two-piece toilet, locate and carefully loosen the nuts holding the toilet tank to the bowl – they’re around the flush valve assembly. Lift the toilet tank off the bowl and keep it somewhere safe.

Step 5: Remove the plastic covers on the toilet’s base to expose the nuts holding down the toilet bowl. Carefully loosen the nuts from the toilet T bolts in the toilet’s base. Rock the bowl gently and unseat it from the toilet floor.

Step 6: With a putty knife, take off the damaged wax ring from the toilet flange. Look carefully at the toilet flange to see if it’s still in good condition. If the toilet flange is in a good condition, we are good to go, otherwise, you need a replacement toilet flange.

Step 7: Insert the new wax ring on the toilet flange. Make sure that the rubber part on the wax ring goes inside the toilet drainpipe. Set the toilet T bolts properly on the toilet flange.

Step 8: Replace the toilet bowl on the toilet flange, ensuring that the toilet T bolts go well into their openings. You may need extra hands to ensure that the toilet bowl seats well on the toilet flange and doesn’t rock. Shaking or rocking the toilet bowl will damage the new wax ring.

Step 9: Gently tighten the nuts on the toilet T bolts until it stands firm. Replace the toilet tank and reconnect the water supply hose.

If you get the procedure right, then you’ve successfully fixed your toilet that’s leaking at the base when your washer drains.

Open the valve to allow water into the toilet tank and flush it a few times. If you don’t notice any leaks, you’re good to go. But if there are still leaks coming out of your toilet when the washer drains, then you may need a professional plumber to help you with proper installation.


To sum up, having a leaking toilet when your washer drains is not a pleasant experience. It puts you at risk.

As such, swift action is required to prevent the situation from getting worse. If you follow the steps outlined above, you’ll be able to fix your leaking toilet when your washer drains without much hassle.

But if you can’t fix it yourself, don’t hesitate to call a professional plumber for help. Good luck!

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