How a Toilet Works in a Basement
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The Physics of Flushing
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Regardless of where a toilet is located, the same components are necessary for flushing and refilling: gravity, suction, and water pressure. Gravity and suction empty the toilet and water under pressure refills it.
When a person flushes a toilet, the lever sets off a series of interdependent events that, for the most part, occur in the tank behind and above the bowl. The position of the tank is not simply aesthetic--its location takes advantage of the pull of gravity and avoids having to use a pump to clear out the waste in the bowl.
Trip Levers and Tank Flappers
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The external flush lever is connected through a hole in the porcelain to another, longer lever called the trip lever. Pushing down on the external lever causes the end of the trip lever to rise, pulling on a chain that connects to the tank flapper. Water pressure in the tank keeps the flapper pressed against the flush valve. When the chain lifts the flapper the water in the tank flows through the flush valve into the toilet bowl. The pressure of the water flowing through the flush valve keeps the flapper from falling back into place.
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Water over the Dam
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Here's where gravity and suction come into play. The the tube which connects the tank to the bowl narrows as it nears the rim of the bowl. This contraction causes the pressure of the water to rise, increasing the speed and force by which it fills the bowl. At the bottom of the bowl, a curved trap is filled with water (which keeps gasses from the sewer from rising up through the toilet). The waste water from the bowl flows up and around the trap's dam and down into the drain pipes. As the water flows over the dam, suction occurs, adding more force to the process and literally pulling the contents of the bowl down the drain.
Refilled and Ready
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As the water flows from the tank, a float that rests atop the water descends with the water flushing the bowl. Once the float falls to a certain point, the shutoff rod attached to the float trips the water supply valve, also known as the ballcock. The tank flapper settles back into place over the flush valve, ending the flow of water to the bowl. Meanwhile, water flows back into the tank through a refill tube. The float rises with the water level, eventually shutting off the ballcock. The toilet is ready for the next flush.
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