What is a Flush Tank?

Mary McMahon
Mary McMahon

A flush tank is a tank which holds fluid in reserve for flushing. The classic example of a flush tank is the tank attached to a toilet. Flush tanks allow for the storage and release of a large volume of water. In addition to being used for toilets, they are sometimes attached to equipment which needs to be cleaned by flushing, and may be used to hold reservoirs of water for dishwashers and similar types of devices.

An example of a flush tank is the tank attached to the toilet.
An example of a flush tank is the tank attached to the toilet.

The flush tank often fills with the assistance of a ballcock, a special type of valve. When the tank empties, the ballcock sinks, opening the valve so that water can enter the tank. As the tank fills, the ballcock rises, eventually floating up above a shutoff point and stopping the flow of water. This allows the tank to fill quickly and automatically.

On toilets, the flush tanks hold a large volume of water that, when flushed, cleans out the bowl.
On toilets, the flush tanks hold a large volume of water that, when flushed, cleans out the bowl.

There are some variations on the basic flush tank design. Some companies make dual flush tanks which allow people to choose how much water is released per flush. For light flushing tasks, only one tank would be activated, while for heavy duty situations, both tanks could be emptied. This saves water by reducing the amount of water used on light flushes, while providing enough water to fully clear a toilet after defecation. The tank can also be adjusted to change the amount of water it holds, which can be used as another water saving measure.

The most common problem which emerges with a flush tank is leakage. Over time, casings and gaskets tend to shrink and change shape, which can allow some seepage. They can also crack. Addressing leakage is important because it can generate a lot of wasted water. In addition, leaks can cause water to pool around the tank, potentially rotting the floor and causing other issues. Some signs that a flush tank is leaking include water around the tank and the sound of running water in the tank when it hasn't been flushed recently.

To repair a leaking flush tank, it will be necessary to turn the supply of water to the tank off; there is usually a shutoff valve on the floor near the tank. Then, the tank should be drained to clear it. With the tank dry, the leaking part can be removed and replaced with a new one. Most hardware stores carry basic flush tank fittings and these fittings are very generic, so it should not be hard to find one which fits a specific tank.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a wiseGEEK researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

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Discussion Comments


@bluespirit - If you look closely at the components in the flush tank try to find a little tube (and is often black). One end of this tube is likely supposed to be where the water is spurting out.

This tube can sometimes come off because of the wet area it is in. But it should be an easy fix with no need to call the plumber for it.

Also another fun tip while you are hanging out in the flush tank, if you fill up a 2 liter bottle with sand or rocks and put it in the flush tank you can save on your water bill because it will need less water to fill your toilet.

Good luck with the spurtage!


I am having a problem with water not seeping out of my flush take but spurting out of the thing that seems to be attached to the ball cock?

Any suggestions or thoughts on why that piece is spurting water now?

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