Find Out What Happens When Your Toilet Flushes

Alison Kasch
Written by Alison Kasch
Updated January 10, 2022
open toilet bowl in home bathroom
Photo: Pixel-Shot/ Adobe Stock


  • A standard toilet flusher uses a drain, fill valve, and siphon jet to flush the toilet with gravity.

  • Automatic toilets use an infrared sensor to detect movement, which flushes the toilet via power and a timed microchip.

  • Dual-flushing toilets use a large trapway to push the proper amount of water down the drain.

  • Many common toilet problems are quick DIY fixes.

  • Call a plumber if you’re unsure what’s up with your toilet.

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Many of us take our toilet for granted in ways we’d rather not discuss. When you think about the alternatives, though, a toilet is truly a beautiful thing. So, what’s going on in there? Here’s everything that makes this wondrous invention flush.

How a Toilet Flushes (The Standard Version)

person holding handle to flush toilet
Photo: Jo Panuwat D/ Adobe Stock

There’s no power plug required for a standard toilet. Instead, gravity flushes the toilet with the help of a drain and fill valve. Here’s a breakdown of how the system works. 

1. Turning the Toilet Handle Moves the Flush Valve

You may have noticed the chain inside your toilet tank attached to the handle. When you turn the handle, it pulls this chain upward and lifts the flush valve. This reveals a small drain hole.

2. Toilet Water Gets Siphoned Away

The hole you see at the bottom of your toilet bowl is technically referred to as a siphon jet. When you flush the toilet, water drains from the tank and enters the toilet bowl at high speeds, resulting in a siphon effect for the remaining wastewater. This effect occurs when wastewater rushes into the siphon hole and through the siphon tube.

3. Wastewater Gets Transferred

Once the wastewater in the toilet gets flushed, it flows through the sanitary sewer system in your area until it reaches a wastewater treatment facility or a septic system.

4. Fill Valve Refills the Bowl and Tank

Once you let go of the flush handle and the toilet tank drains, the flush valve should fall back into place and allow the tank to refill. Water from your home's supply lines enters the toilet tank through the refill valve, which simultaneously fills both the toilet bowl and tank.

5. Float Ball Regulates Water Levels 

Every toilet tank has a floating device inside called a float ball. As the water level in your toilet tank rises, this float ball rises at the same time. At a certain point, the float ball rises high enough to cut the valve off on its own. If this float ball ever becomes detached, it would cause your toilet tank to overflow.

How an Automatic Toilet and Urinal Flush Sensors Work

An automatic toilet flush is hygienic and convenient (albeit a little startling at times). There isn’t a ghost by the toilet. Instead, the device uses infrared beams to detect whenever a user is near. Here’s a breakdown of how a toilet flushes when it’s automatic.

1. Infrared Sensor Detects Movement

An automatic toilet flusher works with a sensor containing two infrared LEDs. One emits infrared beams, while the other receives them. Once the user gets close enough to the toilet, it reflects the infrared light to the receiver.

2. Solenoid Valve Opens the Water Flow

Once the infrared sensor detects movement, it sends a signal to the solenoid valve. This valve will then open up the water flow, sending wastewater out.

3. Power Source Keeps the Toilet Working

Unlike traditional toilets that rely on manual activation and gravity to flush the toilet, an automatic-flush toilet requires power to operate. The three basic types are DC battery, AC power supply, or combined AC/DC. The whole operation gets controlled via a microchip that flushes on a timer.

How a Dual-Flushing Toilet Works

Dual-flush toilets conserve water by having different flush options for solid and liquid waste. Liquids get a half-flush that uses less water. However, the function is a bit different than a regular toilet flush. Let’s have a look at what happens.

1. Each Button Activates a Large Trapway 

Rather than a regular toilet siphoning action, a dual-flushing toilet employs a large trapway, which is the hole at the bottom of the toilet.

2. Wastewater Exits the Toilet Bowl

Depending on which button gets pressed, the trapway pushes the proper amount down the drain. As mentioned previously, this is either a half-flush that uses far less water or a full flush. The full flush still uses less water than traditional toilets due to the efficiency of the trapway.

As wonderful as they are, toilets can malfunction from time to time. Luckily, many common problems are simple DIY toilet fixes. You might also hear a noise in the wall when the toilet flushes, which could indicate a few different issues. 

Depending on what has gone wrong, you may need to replace the toilet, get it repaired, or execute some troubleshooting. There are some helpful how-to's online, but get in touch with a top-rated local plumber if you're in over your head.

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