How to Fix a Toilet that Leaks When Flushed

One of the most prevalent plumbing problems experienced by homeowners is the occurrence of leaks, which can affect a variety of fixtures, including toilets. Despite the fact that toilets are designed to last for many years with minimal maintenance, there may be instances when leaks may arise at the base during flushing.

When this occurs, water may spill onto the floor, causing significant water damage. It is important to note, however, that such leaks can be addressed without requiring the services of a professional plumber, even for those with no prior plumbing experience.

Therefore, a leaky toilet does not necessarily signify the end of its usability, as prompt action can effectively mitigate the issue.

What Causes a Toilet to Leak When Flushed?

When you flush your toilet, water leakage at the base is a common issue that can be caused by a variety of factors. Typically, a faulty seal beneath the toilet is the primary cause of this leakage, which can be confirmed by observing water accumulation around the base of the toilet.

However, in some instances, the source of the leakage may not be the seal, and you may need to identify the specific problem area within your toilet. To do this, use a sponge to absorb any water on the floor around the toilet and dry the area with a towel.

Then, keep an eye out for new puddles of water forming on the floor and check if the water is originating from beneath the toilet. Other factors that can cause leakage when the toilet is flushed include a defective shutoff valve, a loose supply tube, sweating (condensation), or a cracked tank.

It is important to address the root cause of the leakage promptly to avoid water damage to your bathroom and potential health hazards. Therefore, you may consider seeking the assistance of a professional plumber if you are unable to locate the source of the problem or if the issue persists despite your efforts to fix it.

Other Causes of the Leak

Condensation, a natural phenomenon, occurs when water vapor transforms into liquid droplets upon contact with a colder surface.

In the case of toilets, this process is commonly referred to as “sweating.” Sweating occurs when the temperature inside the tank of the toilet is colder than the temperature outside the tank in the washroom, causing moisture to form on the exterior of the tank and subsequently drip onto the toilet floor.

This problem is more prevalent during the summer months, but it can happen at any time of the year, given the right conditions. One solution to this problem is to use tank liners to insulate the cold water inside the tank from the warm air outside.

Another solution is to install anti-sweat tank valves, which mix warm and cold water to reduce the temperature difference between the inside and outside of the tank.

By employing either of these solutions, you can effectively manage condensation and prevent water damage to your bathroom floor.

Leakage from between the toilet bowl and the tank:

To determine the source of a toilet leak, a colored water test can be employed. When water is seen trickling between the tank and bowl near the center, it may indicate the need for a new tank-to-bowl sponge gasket or replacement washers for the bolts in that area.

If the leak stems from the gasket between the tank and bowl, it will typically manifest more frequently during toilet flushes. When washers and bolts have failed, the leak will likely appear nearer to the sides of the bowl, far from the center and close to the edge.

To rectify the issue, it is necessary to separate the toilet tank from the bowl and replace the sponge gasket or washers as needed. The repair process and necessary parts may vary depending on the make and model of your toilet.

Leakage from inside the tank of the toilet:

To determine whether a toilet tank is leaking, it is recommended that you carefully remove the tank lid, as it can be fragile and slippery when wet. Next, introduce a few drops of organic-based coloring, such as food color, into the water in the toilet tank.

Allow the water to settle and change color for a period of 15 minutes. If any colored water is observed in the tank, it is indicative of leakage. This will highlight the areas that are affected. The necessary action to replace the tank will be required at this point.

Fill valve (ballcock) shank gasket leak:

The water tank valve is responsible for controlling the flow of water into the tank, and is secured to the shank gasket inside the tank. To determine the type of leak, a colored water test can be performed. Inspect the porcelain surrounding the gasket for any signs of cracks.

In the event that no damage is detected, the leakage issue can usually be resolved by tightening the shank nut situated beneath the tank.

Gradually tighten the nut by a quarter turn at a time, and carefully observe whether any further leaks are present. If the problem persists even after this fix, it may be necessary to replace the gasket.

Gasket problems:

To determine whether a leaking toilet is caused by a faulty gasket, it is necessary to disconnect the toilet tank from the rest of the unit. This process can be somewhat intricate and requires the assistance of a second person. To begin, turn off the water supply and flush the tank until it is completely empty.

Next, loosen the nuts that secure the hold-down bolts, taking care to hold the bolt top in place with a screwdriver while using a wrench to loosen the nuts. Once the nuts have been removed, loosen the water supply line nut that secures the tank and carefully remove the tank from the bowl.

Inspect the rubber gasket for any cracks or signs of dryness. If you observe either of these issues, the solution is to replace the gasket with a new one.

Leaking supply line:

There may be several reasons why your toilet is leaking water, but one potential culprit is the nuts at the connection points of the supply line. These nuts are typically found at both ends of the line, where it attaches to the inlet of the toilet’s ballcock and the shut-off valve on the wall.

If you have a rigid supply line, the problem may be a worn-out washer, which can be replaced to solve the issue. However, if your supply line is a single-piece unit attached directly to the shut-off valve, it may be more practical to switch to flexible stainless steel water flexes that are easy to attach and reliable.

Alternatively, you can replace the single-piece unit with a separate, flexible supply line and shut-off valve, which can provide greater flexibility and ease of maintenance. By taking these steps, you can effectively address the leaking water issue and ensure that your toilet operates smoothly and efficiently.

Flapper problems:

The flapper is a vital component of the toilet responsible for lifting when flushed and releasing from the valve seat to allow water to flow through the tank and into the bowl to push waste away. However, if the flapper is not in its proper position, the toilet may not function optimally, as water will leak through the tank.

To rectify this issue, you will need to turn off the water supply through the shut-off valve and empty the water from the tank by flushing the toilet. To avoid any mess, place a bucket under the tank to collect any water that escapes, and clean up any water that spills onto the floor.

Next, remove the lid of the toilet tank and inspect the flapper. If you notice that the rubber has become hard and inflexible, it is time to replace it. To do this, detach the old flapper from the chains leading to the flush handle and snap it out of place.

Then, pop the new flapper into position and attach it to the chain of the flush handle. Once complete, turn on the water and fill the tank.

By following these simple steps, you can effectively replace a faulty flapper, ensuring that your toilet functions smoothly and without any leaks.

Leaking shut-off valve:

The shut-off valve in your bathroom is equipped with a pipe connection that is located in close proximity to the wall. It is possible that water can seep out from this pipe connection, resulting in leakage. If this occurs, the valve will need to be replaced.

However, in some cases, tightening the valve onto the pipe may be a viable solution, depending on the type of pipe or valve that is installed in your bathroom.

It is important to carefully consider the appropriate course of action to prevent any further damage and ensure the proper functioning of your bathroom’s plumbing system.

How to Fix a Toilet that Leaks when Flushed

Repairing a leaking toilet at the base after flushing is a task that can be accomplished with ease. By following a few simple steps, you can fix the problem by tightening the closet bolts that secure the toilet to the floor.

Firstly, remove the caps covering the bolts with either a slotted screwdriver or a putty knife. Using a wrench, tighten each bolt alternately, one at a time.

Be cautious not to apply too much pressure to prevent cracking the toilet’s base. If this process does not eliminate the leakage, it is necessary to remove the toilet and replace the wax gasket.

Here is a step-by-step guide for installing a new wax ring to ensure a water-tight seal between the closet flange and the toilet. The procedure is straightforward and easy to follow.

The initial step to replace a wax gasket involves turning off the water supply at the shut-off valve, which can typically be found beneath the toilet in the crawl space or basement.

It is essential to ensure that the handle is turned fully clockwise. Next, remove the tank lid and flush the toilet to drain the water from the tank. Use a sponge to remove the remaining water from the tank and a small paper cup to get rid of the water in the toilet bowl.

The next step is to disconnect the tube that supplies water by loosening the compression nut located on the shut-off valve. Try to disconnect it by hand before using a wrench.

The following step is to remove the nuts from the closet bowl by removing the caps and using a wrench. If the bolts spin as you turn the nut, use needlenose pliers to grasp the top. If the bolts are rusted or cannot be removed, carefully cut the nuts off using a mini-hacksaw to avoid damaging the toilet’s body.

To remove the toilet bowl, gently rock the toilet back and forth, grab the rim of the toilet bowl and lift it from the floor.

Place the toilet on a cardboard piece, newspaper, or blanket, and plug off the drainpipe with a towel or rag to prevent sewage gasses from escaping into the bathroom. Remove the old wax ring and dispose of it properly since it cannot be recycled.

Scrape off the old wax gasket from the toilet’s bottom and the closet flange on the floor using a putty knife. Inspect the flange to ensure that it is not bent or cracked. If the flange is damaged, replace it or use a repair strap to fill the missing piece.

The next step involves installing the curved metal strap. Begin by loosening the screws that hold the flange in place on the toilet floor, then insert a new closet bolt into the slot of the strap.

Tighten the screws of the flange to secure the strap in place. Install the remainder of the bolts in the flange, and if they do not stand upright, pack some wax around the base of each bolt.

If you want the wax ring to slide easily into the outlet of the toilet, leave it in the sun for a while or dip it in warm water for a few minutes. If you had cut off your old bolts, replace them with new ones. Set a new wax gasket on the closet flange, ensuring that it is perfectly centered.

When replacing the toilet, consider upgrading your plumbing with a flexible stainless steel-enmeshed polymer supply tube that is easier to install and more durable than an old-fashioned chrome-plated copper water supply tube.

Apply a light coating of pipe joint compound at the ends of the water supply tube and tighten the end that leads to the ballcock shank that protrudes from the toilet tank’s bottom.

To set the toilet back in place, grip the bowl at the hinges of the seat, then lift the toilet to the flange. Place the toilet on the wax gasket using the closet bolts as guidelines. Ensure that the washers are set over the bolts and that the nuts are tightly threaded on.

Press down the nuts on the bowl’s rim to compress the gasket before tightening the bolts. Alternatively, you can tighten each bolt until each feels snug, then press down the toilet bowl, and once again tighten the nuts, avoiding exerting too much pressure as it could crack the toilet. Ensure that the tank is parallel with the back of the wall.

Cut the closet bolt with a hacksaw, and snap bolt caps on the bolts. The final step is to tighten the end of the water supply tube that connects to the shut-off valve that is loose. Ensure that the valve is open, and flush the toilet a couple of times.


Toilet leaks are a common occurrence that can cause anxiety when experienced in your bathroom during flushing. However, there’s no need to worry as there are various reasons why a toilet may leak, and each problem has a solution that can be easily resolved. In some cases, you may need to replace a damaged part with a new one.

It’s crucial to identify the specific cause of the leak before attempting to fix or replace any parts. By doing so, you’ll be able to determine the appropriate course of action to take to ensure that your toilet functions properly.

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