How Does a Flushing Toilet Work?


The toilet is not typically discussed at dinner parties, but it is a part of everyone's life. As a matter of fact, the toilet is a household item that’s often taken for granted until it doesn’t work. When the flushing mechanism malfunctions, the water backs up, the wax ring no longer seals or the stopper inside the tank lets a bit of water slowly leak out. In such cases we start to think about the simple but ingenious way a flushing toilet works.

Toilet Parts

  • The basic components of a toilet include the tank, which is made of vitreous china and holds a large quantity of water; the bowl, also made of vitreous china, which holds the waste until flushed away; the flush mechanism, which makes it possible for the water from the tank to enter the bowl; and the water, which helps all of those components do their jobs.

Flush Mechanism

  • The flush mechanism, located inside the tank, comprises a lever or button, a bar, chain, float and rubber tank ball or flapper that plugs the hole in the bottom of the tank so the water doesn’t leak into the bowl prematurely. When the lever is pushed, the bar lifts the chain, which in turn pulls up on the tank ball/flapper, allowing the water to rush out of the tank and into the bowl. The float comes into play later, as the tank refills with water.

Siphon Effect

  • When the water rushes from the toilet's tank into the bowl, through tiny holes all along the rim, it creates downward pressure, pushing the water from the bowl into the plumbing at the base of the bowl. The elongated S-shaped plumbing acts as a siphon, pulling the water down and out of the bowl and into the pipes in the floor below the toilet.

S Trap

  • The water stops siphoning from the toilet when there is very little left in the bowl, allowing air to break the siphon seal. The S trap at the bottom of the toilet always is filled with water. This trap creates a liquid seal that keeps odors and gas from rising from the sewer pipes into the bathroom. In addition, a wax seal, located where the toilet meets the bathroom floor, keeps water from leaking out when the toilet is flushed and also keeps odors from entering the room.

Fill Valve

  • As the water rushes from the tank, it allows the tank float to drop, causing the tank ball or flapper to cover the drain opening and activate the fill valve. The fill valve, fed with fresh water from a water line in the base of the tank, opens and allows water to run into the tank, filling it for the next flush. As the tank fills with fresh water, the float rises, closing the fill valve. The toilet is now filled and ready for the next flush

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