How A Toilet Works

By Gillian Burdett

Toilet technology continues to evolve. The modern toilet has eliminated the need to run outside to the privy every time nature calls, and, thankfully, sloppy chamber pots are now museum pieces. From the water-conserving low-flush toilets introduced in the ’90s to today’s sensor-activated flushes, toilets are changing to better fit our lifestyles. Plumbing supply manufacturers now offer models with heated seats, integrated bidets and motion-activated lids. However, the basic function of a toilet, to quickly and safely carry away waste, still relies on a major law of physics – gravity.

The parts of a toilet

For residential use, toilets with a tank and a bowl are most common. You may be familiar with tankless models often found in public restrooms. These rely on a high-pressure water supply not usually found in private homes.

The toilet’s tank stores the water needed for flushing, and it contains the mechanisms to flush and refill the tank. There are variations on these mechanisms, not all tank innards look the same, but they will include a flush valve and fill valve, a flapper, a float and an overflow tube.

The bowl is where the magic happens. It is rimmed with a flush passage, which has small holes from which the tank’s water, upon flushing, shoots out in jets. This action cleans the sides of the bowl while raising the bowl’s water level. An inverted u-shaped trap is encased in the toilet base and serves as the bowl’s drain pipe.

How the flush happens

The handle, or push button, mounted on the outside of the tank operates a lever that lifts the flapper from the tank’s outlet valve. This, in turn, releases the stored water into the bowl’s flush passage. As the water level in the bowl rises, the water in the drain pipe rises until it reaches the tipping point, the top of the u-shape. Gravity then pulls the wastewater down, creating a siphon that empties the bowl and pulls the wastewater out through the sewer line.

Refilling the tank

When the tank empties, the float or ball inside the tank drops, which causes the fill valve to open.  Fresh water begins to refill the tank through the overflow tube. As the water rises in the tank, the float rises as well. Once the float is raised to its original position, it shuts off the fill valve.

When a toilet isn’t working properly

A toilet will function well for years with minimum maintenance. Some problems you may be able to prevent or correct yourself. Regularly scrubbing under the rim of the bowl will help prevent lime deposit buildup that can clog the rim holes and cause a slow flush. A toilet that continually runs may simply need an adjustment to the float or flapper. In areas with hard water, the parts of the tank’s inner works may corrode. Replacing these is a fairly simple task.

Other issues may require a pro. A leak from underneath the toilet may indicate a failure of the wax ring that seals the connection between the toilet and the drainpipe. Replacing the wax ring requires shutting off the water supply and unbolting the toilet from the floor. You may prefer to bring in an expert for this work. You need to call a plumber if you smell sewer gases in your home. These gases are a health hazard and may indicate a problem with your plumbing ventilation system.

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