How a Standard Gravity Flush Toilet Works

  • 01 of 04


    Steve Hallo

    The standard toilet most of us grew up with is known as a gravity-flush toilet, meaning that it does its work simply by the force of gravity on the water and has no pressure assistance of any kind. While pressure-assisted toilets are becoming more common, the standard gravity-flush design is still by far the most common in most residential homes. With a simple design and relatively few moving parts, repairs are quite easy. The lack of any mechanical parts (like those found in pressure-assisted...MORE toilets) makes the repairs fairly inexpensive as well.

    The toilet works on principals of gravity, hence the name. Let's take a look at what happens when the toilet is flushed. 

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  • 02 of 04

    Water from the Tank is Released

    Steve Hallo

    When the handle of the toilet is pushed, the flush lever inside the tank attached to a lift chain lifts up a flapper valve at the bottom of the tank, allowing water to rush down through the flush opening and into the toilet bowl. The forceful action of the water is what forces waste in the toilet bowl down into the toilet trap and into the house drain system and from there out to the sewer lines. 

    What Can Go Wrong 

    • A loose or disconnected lift chain joining the lift arm to the flapper valve can...MORE cause the toilet handle to simply jiggle and not flush the toilet at all. 
    • A loose handle mounting nut can cause the handle to wiggle loosely when depressed. 
    • If the lift chain is too long, the flapper valve will not lift up high enough, and the toilet flush may be incomplete or may require that you hold down the handle for several seconds in order to flush completely. 

    Water housed in a tank above the bowl is released into the bowl, causing water to push through the trap, thus emptying the bowl of its contents.When the handle is pushed down the lever arm pulls the flapper chain up. The flapper then lifts, releasing the water in the tank into the bowl. As the tank empties with water, flapper goes down.

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  • 03 of 04

    During the Flush

    Steve Hallo

    As the tank empties with water, the float ball or float cup in the tank goes down, causing the flush valve (sometimes called a ballcock) to activate the flush valve to begin refilling the tank. It also starts spraying water into the fill tube, which leads to the bowl. At the same time, a refill tube running from the flush valve to the overflow tube sends a small stream of water down into the toilet bowl, refilling the level of standing water there. 

    What Can Go Wrong 

    • If the refill tube slips away...MORE from the overflow tube, no water will go down into the toilet bowl, and it will not refill with standing water. 
    • If the flapper valve is worn or misaligned, it will not reseat in the flush valve after the flush, and water will continue to leak down into the bowl; the toilet valve will continue to run because the tank never fills up. 
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  • 04 of 04

    After the Flush Cycle

    Steve Hallo

    As the water level in the tank rises, the float ball or float cup shuts off the toilet valve and water stops entering the tank. The toilet is ready for the next flush. 

    What Can Go Wrong 

    • If the flush valve is not adjusted properly, the level of water in the tank may climb too high, which causes water to spill over into the overflow tube. The toilet will continue to run constantly. Or, if the water level in the tank is too low, the toilet will flush incompletely, failing to completely empty the...MORE toilet bowl  of waste.