How Long Should it Take to Fill a Toilet Tank? [Fix a Slow-Filling Toilet]

The average toilet tank takes one to three minutes to fill after flushing. If your toilet is taking longer than three minutes to fill, or if the water runs continually without filling the tank, then you need to inspect the toilet more closely to find out the source of the problem. Start by inspecting the water supply line to ensure the toilet is getting adequate water. If the water supply isn’t the problem, remove the toilet tank lid to make sure the float, flapper, and fill valve are operating properly.

How long should it take to fill a toilet tank?

How Much Water Should Be in a Toilet Tank?

Interior of toilet tank showing float, overflow tube, and flapper. The overflow tube is highlighted and labeled.
The water level should be 1 inch below the top of the overflow tube when the toilet tank is full.

The typical home toilet tank holds one to 3.5 gallons of water. However, this number doesn’t do you much good when you’re inspecting your toilet to see if it is filling properly. To figure out if your tank is as full as it should be, remove the tank lid. Look for an open-topped tube that comes up from the bottom of your tank and rises up out of the water. This is your overflow tube. The water level in the tank should be just below the top of the overflow tube.

If the water level in the tank is more than one inch (2.5 cm) below the top of the overflow tube, the level is too low. This will lead to a partially empty tank and poor flushing. Usually, water level can be corrected by adjusting the float/fill valve assembly in the tank.

4 Ways to To Troubleshoot a Slow-Filling Toilet Tank

A slow-filling toilet tank can often be fixed without the aid of a plumber. Before you call an expert, try these methods. It can be relatively quick and easy to repair a slow-filling tank. In just a few minutes, you can have a fully operational toilet.

1. Check the Water Supply

A man's hand checking the water supply on a toilet before seeing how long it takes to fill up.
Check to make sure your toilet’s water supply is open.

Before going any further, check the water supply valve. This is the handle on the water line that feeds water into the tank. It is usually located on a pipe outside the toilet, coming from the floor. First, turn the handle counterclockwise to make sure the water supply valve is fully open. A partially closed valve restricts the flow of water to the tank, contributing to slow filling.

  • Turn the water supply valve counterclockwise to make sure it is fully open. This can increase water flow to the tank and speed up the filling.
  • If the tank is filling slowly even when the water supply valve is open, turn off the water supply and unhook it.
  • Once the water supply line is unhooked, direct it into a bucket and turn the valve on again.
  • If the water flowing from the supply line into the bucket has poor pressure, this is a sign of a plumbing problem that is best solved by a professional.
  • If the water flows with steady pressure out of the line and into the bucket, the issue is not the supply line. Reattach the water supply to the toilet and begin troubleshooting components in the toilet tank.

If the tank is filling slowly even when the water supply valve is fully open, there’s a different issue at play. To further troubleshoot your water supply, turn the valve clockwise to shut it off. Then, unhook it from the toilet. Direct the water line into a bucket and open the valve again. Observe the flow of water. If it is a steady stream with good water pressure, then it is operating as intended. If there is weak water pressure, this indicates a plumbing problem that should be addressed by a plumber.

2. Adjust the Float and Fill Valve

Man wearing orange gloves adjusting the fill valve control inside an open toilet tank.
Turn the fill valve counterclockwise to lower the water level and encourage your toilet tank to fill more quickly.

The float is the mechanism that tells the toilet to start and stop filling. It is designed to float on top of the water in the tank. When it is raised high enough by the water, it signals filling to stop. If the float is poorly adjusted, it may cause the toilet to continue running indefinitely, or it may signal the toilet to stop running before the tank is full.

  • Remove the lid of the toilet and locate the float.
  • Your float may be a ball cock assembly, which is a hollow plastic ball at the end of a metal arm. Alternatively, you may have a float cup, which is a plastic cylinder around the fill tube on the left side of the toilet tank.
  • Adjust a ball cock float by tightening or loosening the screw where the metal arm attaches to the top of the fill valve.
  • Adjust a float cup by tightening or loosening the screw at the top of the fill valve.

Floats come in two main varieties. The first is the ball cock variety, which is a hollow plastic ball at the end of a thin metal arm. The second is the float cup variety, which looks like a small cylindrical buoy around the fill tube (the tube on the left-hand side of the tank). To adjust either of these floats, locate the adjustment screw at the top of the fill valve and tighten or loosen it. This will determine where the float stops and signals water to cease flowing into the tank.

3. Inspect the Flapper

Closeup of the interior of a toilet tank with the flapper circled and highlighted.
An old or damaged flapper can cause your tank to fill slowly or run on-and-off.

A common cause of an improperly filling toilet tank is a malfunctioning flapper. The flapper is the rubber flap (usually red) at the bottom of the toilet tank. It is attached at the bottom of the overflow tube and has a chain that runs from the top of the flapper to the end of the flush lever. If your toilet flapper is not sealing properly, or if the chain is too short, water will continually flow through the hole beneath the flapper, into the toilet bowl. A tank with a bad flapper will run for a long time as it struggles to fill.

  • Locate the flapper inside the toilet tank. It is usually a red rubber flap with a chain running from the top of the flap to the flush handle lever.
  • The flapper is designed to seal off the hole between the tank and bowl between flushes.
  • If the flapper has a poor seal, this can cause water to slowly leak into the bowl.
  • If water leaks around a bad flapper, the toilet will have to run longer to fill the tank, may stop and start filling periodically, or may run nonstop.
  • Replace a bad flapper with a new toilet flapper.

Replacing a toilet flapper is an easy fix for toilets that won’t fill properly. Just turn off the water, flush the toilet, and then unhook the existing flapper from the overflow tube and chain before replacing it with a new one. Most rubberized toilet flappers pull off easily.

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4. Clean the Tank Components

Man pouring CLR into a toilet tank where the toilet tank lid has been removed.
Add CLR to your toilet tank to remove buildup and allow the tank to fill faster.

Because so much water flows through a toilet, sediment, grime, and calcium buildup is likely to form on your fill valve and other components. A good cleaning can remove this buildup and cause water to flow into your toilet tank much faster. The best way to clean toilet tank components is:

  • Remove the toilet tank lid. Mark where the water level is when the tank is full.
  • Turn off the water to the toilet tank and flush the toilet to empty it.
  • Use a toothbrush dipped in either vinegar or CLR to scrub the fill valve and any other tank components that are above the water level when the tank is full.
  • Fill the tank 1/4 of the way to the fill line with CLR.
  • Turn on the water to the tank. Allow it to fill with water/CLR mixture.
  • Do not flush the toilet for 4–8 hours. Allow the CLR mixture to soak and break down the buildup before flushing.

Once you’ve completed this, resume using your toilet as usual. This process can truly help break down calcium and grime that clogs fill valves, floats, and other toilet components.

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Why Does Your Toilet Tank Take So Long to Fill Up?

A slow-filling toilet tank is usually caused by one of the following:

  • Poor water supply, including lack of water pressure from the supply line.
  • Improper adjustment to the fill valve/float assembly.
  • A poorly sealed flapper.
  • Calcium and sediment buildup in the tank.

In most cases, these issues can be solved quickly, with simple tools. Often, adjusting a fill valve or replacing an old flapper will help your slow-filling toilet fill quickly and retain water in the tank.

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