Toilet Leaks When Flushed: 4 Common Causes (with Fixes) - Think Tank Home (2024)

If your toilet leaks when its flushed, chances are the problem is either a faulty toilet fill valve or the wax seal that forms a seal between the toilet and the sewer line. Identifying the problem is as easy as determining if the water is leaking from the tank or the base of the toilet.

Fixing either of these problems is inexpensive and relatively easy, but if you don't enjoy DIY projects you can always call a plumber. This article will help you identify the reason your toilet leaks after being flushed and take you step-by-step on how to fix the leak.

If your toilet leaks when its flushed and water is spraying inside the tank, then the most likely cause is a faulty fill valve. Fill valves (also called ballco*ck valves) are responsible for filling your tank full of water.

When the toilet is flushed, the water in the tank fills the toilet bowl. Once the tank is empty, the fill valve turns on and brings water from the water supply into the tank. Water flows through the base of the valve and through the refill tube to the overflow tube. As the water rises within the tank, the float on the fill valve shuts off the water supply once the water reaches the fill line.

You may notice water dripping from the flush handle or a small puddle of water around your toilet, but you'll almost certainly notice your toilet making a different sound as it fills the tank. Chances are, if you remove the tank lid, you'll find water spraying upwards.

In most cases, the line connected to the overflow tube is either misaligned or damaged. If its misaligned, simply move it so the water flows from the line into the overflow tube.

If it is damaged, you'll probably need to replace your fill valve. To learn more able fill valves click here.

Of course, you can always call a professional plumber, but fill valves are relatively inexpensive and easy to replace. Just make sure you find the right one for your toilet.

How to Replace a Fill Valve

Step One - Empty the Tank

• Turn off the water supply and disconnect the supply line from the bottom of the toilet.
• Flush the toilet to empty the tank.
• Remove the tank cover.
• Use a shop vac or sponge to remove the excess water within the tank.

Step Two - Remove the Fill Valve

• Remove the locking nut to the fill valve.
• Remove the fill valve.

Step Three - Prep the New Fill Valve

• Adjust your new fill valve. The marking on top should be at least 1" above the overflow tube. (Follow the directions on your fill valve as they may be different).

Step Four - Install the New Fill Valve

• Insert the fill valve into the tank so the shank protrudes through the bottom of the tank.
• Connect the locking nut to the fill valve's shank so that it fits snuggly.

Step Five - Fill the Tank

• Trim the refill tube (if necessary), then attach it to the overflow tube.
• Connect the water supply line to the toilet. Turn the water on.
• As the tank fills, check the water level and adjust the fill valve's height as needed.
• Check for leaks.

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If you notice water along the base of your toilet, chances are the wax ring needs to be replaced. A toilet wax ring creates a watertight seal between the sewer pipe and the bottom of the toilet. Its made of sticky wax and requires no maintenance and can last 30+ years!

In most cases, the wax ring will only need to be replaced when you purchase a new toilet or do a bathroom remodel where the floor is replaced.

Although, occasionally wax rings will dry out and no longer be able to create a seal from the toilet to the sewer pipe. When this happens, your toilet will leak when it's flushed and you'll notice a puddle of water on the floor.

You may also notice a slight rocking from side-to-side when you're sitting on the toilet. This could be a sign that the wax ring is losing its grip and needs to be replaced.

Replacing the wax seal isn't especially difficult and, provided you have a few basic tools, you'll likely spend less than $20 in parts. With that said, many homeowners are uncomfortable "pulling" their toilets and prefer to hire a plumber to fix the problem.

Wax Ring vs Non-Wax Ring

A toilet wax ring is made of sticky wax that creates a seal when its crushed into place by the toilet. Basically, the wax fills all the gaps to prevent leakage when you flush as the waste water travels from the toilet to the sewer pipe.

The wax ring is the most traditional method to seal your toilet and prevent leakage, however, there are wax-free seals available. Non-wax seals are a relatively new product and have not been time-tested, but they are far less messy than wax rings, and they can be reused should you need to pull your toilet in the future.

This video covers both types and can help you make the best buying decision for your situation.

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How to Replace a Toilet Wax Seal

Once you buy a new wax seal or, if you choose to use a wax-free seal, you're ready to get started. Here's what to do:

Step One - Drain the Tank

• Turn off the water supply to the toilet by closing the toilet shut-off valve.
• Flush the toilet and hold down the lever to drain the tank.
• To remove the remaining water in the tank, you can use a shop vac or a sponge. You can also use a plunger to help drain the toilet bowl.
• Once the tank is dry, disconnect the water supply line from the bottom of the tank. Have a towel handy as some water will drain from the tank and line.

Step Two - Remove the Toilet

• At the base of the toilet pop-off the protective caps.
• Using an adjustable wrench remove the bolts and washers.
• Gently rock the toilet from side-to-side to loosen the seal.
• Lift the toilet straight up and set it aside, preferably on old towels or a tarp.

Step Three - Remove the Old Wax Seal

• It's a best practice to cover the sewer pipe with an old rag to prevent sewer gases from escaping.
• Remove as much of the old wax gasket as possible from both the floor's pipe fitting (called toilet flange) and the bottom of the toilet with a putty knife.
• The toilet flange should be completely clean and dry before installing a new wax seal. Call a plumber if the flange is damaged.

Step Four - Install New Wax Seal

• Before installing your new wax seal, be sure to read the instructions on the package. Some are self-adhesive and there may be other small differences that you'll need to be aware of when installing.
• Although, this may vary from brand-to-brand, in most cases you can decide whether you're more comfortable installing the wax seal to the bottom of the toilet or the top of the flange first.
• Once the wax seal is centered in position, lower the toilet onto the flange. Go slow and line-up the toilet's bolt holes to the holes on the flange.

Step Five - Seal the Wax Seal in Place

• Once the toilet is firmly seated on the flange. Use your body weight to compress the wax and seal the toilet to the floor. Do this by closing the lid and sitting down. You can shift your weight back-and-forth and from side-to-side without rocking.
• Once the toilet's base is flush with the floor, use the bolts and washers to secure the toilet in place.
• Connect the water supply line to the tank and open the supply line valve.
• When the tank fills with water, flush the toilet 2 or 3 times to ensure there are no signs of leakage.

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Whenever water is traveling through the toilet's components there's an opportunity for leakage. The weak part with a small and nearly undetectable drip, may begin dripping larger quantities of water onto your floor when flushed.

Chances are, if your water supply lines are leaking the problem won't be just when you flush the toilet, however, it may be more noticeable when the tank is filling.

The water supply line connects your toilet tank to the plumbing. It's not uncommon for the water supply line or it's fitting to develop leaks, and many plumbers recommend swapping them out periodically.

If you don't have a noticeable leak, you can grab a towel and wipe down the water supply line and the fitting to the tank as well as the water shutoff valve. At this point, you may see water seeping from the fittings or even the line itself.

If you don't, you can flush the toilet and observe while the tank fills. If there are any leaks in your water supply line or fittings, they will almost certainly show up after flushing.

Water Supply Line Solutions

The problem could be as simple as a loose fitting that can be tighten with a wrench. Or you may need to replace the toilet shut-off valve, although typically that issue doesn't just occur during flushing.

It's more likely you'll need to replace your water supply line. This is a relatively inexpensive and easy fix which you should be able to do yourself. But before you change it out, try to tighten the fittings.

Grab a wrench and turn a quarter of a turn on the fitting that connects to the toilet shut-off valve, and tighten by hand the connection that connects to the tank.

If there's still a leak, or the hose itself if leaking, you'll need to replace the water supply line. Check your fitting sizes to ensure you purchase the correct one for your toilet, or you can pick up a universal water supply line which will fit the majority of different fitting sizes.

How to Replace a Water Supply Line

• Turn off the water supply to the toilet by turning the toilet shut-off valve.
• Remove the fitting that connects to the base of the toilet. Typically it is only hand tight, but in some cases, you may need to use pliers or channel locks. It's a good idea to have a small bucket or towels when removing the fitting from the toilet.
• With a pair of pliers, remove the fitting that connects the water supply line to the shut-off valve.
• Install the new water supply line compression fitting onto the shut-off valve. Tighten by hand and then with a crescent wrench until the nut is snug. Do not over tighten.
• Hand tighten the connection fitting to the tank until you hear a click. Again, do not over tighten.
• Turn the water back on and check for leaks.

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The tank-to-bowl gasket provides a seal between the toilet bowl and the tank. If your toilet tank-to-bowl gasket is faulty you'll notice leaky at the base of your toilet tank that may even puddle onto the floor.

When a tank-to-bowl gasket fails, you'll normally have a constant seeping type of a leak, not necessary a leak when you flush your toilet. However, when the water is moved from the tank to the toilet bowl and the tank refills, you may notice more water leaking from the gasket.

How to Replace a Tank-to-Bowl Gasket

Step One - Drain the Tank

• Turn off the water supply to the toilet by closing the toilet shut-off valve.
• Flush the toilet to drain the water in the tank.
• Use a shop vac or a sponge to remove the remaining water. You can also use a plunger to help drain the toilet bowl.
• Once the tank is dry, disconnect the water supply line from the bottom of the tank. Have a towel handy as some water will drain from the tank and line.

Step Two - Remove the Tank

• Remove the bolts from the bottom of the tank. Typically there are two bolts, but some toilets use three.
• Gently lift the tank from the toilet. You may need to rock it from side-to-side slightly.
• Set the tank on its side. Keep in mine that there may still be some water inside the tank, so you may want to set it on some towels.

Step Three - Replace the Tank-to-Bowl Gasket

• Remove the old tank-to-bowl gasket from the flush valve and remove the bolts.
• Use a towel to clean the area.
• Place the new tank-to-bowl gasket over the flush valve.
• Install the new tank bolts from inside the tank.

Step Four - Replace the Tank

• Lift the tank and place it back onto the toilet bowl. The bolts should align with the bolt holes.
• Connect the washers and nuts to the bolts to secure the tank in place. Only tighten by hand.
• Once both bolts are hand tightened, use a wrench and tighten each bolt. Rotate between the bolts until they are each tight enough to secure the tank.
• Connect the water supply line to the bottom of the tank and turn on the water.
• When the tank is full, flush the toilet. Check for leaks, especially where the bolts are seated.

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