How Does a Toilet Flush Work? | Understanding Your Bathroom

Have you ever ended a bathroom trip by sitting back and asking yourself how the toilet works? If so, you’re not alone. While we all use the toilet on a day-to-day basis, not everyone understands the simple magic that’s behind flushing toilets.

toilet flushing water

Today, we’re going to take a look at the physics behind flushing a conventional toilet as well as talk about the parts of a toilet tank. It’s time to learn about the most-used fixture in your bathroom!

Inside the Tank

First, let’s go into the parts of the typical toilet cistern, the tank where the water for each flush is stored. There are different kinds of flush toilets (dual flush toilets, low flow toilets, pressure-assist toilets) but they use the same or similar toilet parts as conventional flush toilets. So, unless you’re using composting toilets or vacuum toilets, the process will use the same kind of flushing mechanism.

Plus, it’s good to know these parts because if you have a problem with your toilet, it will most likely be open of these parts!

  • Tank Level/Flush Handle – This is the flush lever or button that you push to initiate the flush. On a dual flush toilet, you have two to conserve water.
  • Toilet Flapper Valve– The rubber flapper valve covers the flush valve and is connected to the tank level by a chain.
  • Flush Valve -Water flows out of the tank and into the bowl when you flush the toilet, and it does so through this outlet pipe. Water flowing through this valve creates a power flush.
  • Fill Valve – This is connected to the water supply and refills the water tank through a tube that runs into the overflow tube.
  • Float -In the tank, water rises and falls as the toilet works. The float sits on top of the

The Physics Behind a Toilet Flush

Toilets are designed to store water in the tank above the bowl. When you flush your toilet, the tank pushes water into the bowl at high speed through small holes around the rim of the bowl. When the water rises, the waste sitting at the bottom of the bowl is pushed down through an S-trap, disposing of the waste.

As the water stops filling up the bowl and the pressure lowers, the water stops getting pushed up through the S-bend, and that is how the bowl refills.

The Flushing Process

There are five simple steps to flushing a toilet, from removing the waste to refilling the tank. Let’s take a look:

open toilet flapper valve
  • Step 1 -The Handle Opens the Flapper: To start everything off, you have to push down the handle on the outside of the toilet cistern. What this does is lift the flapper on top of the cistern so water can begin to flow into the bowl through the flush valve.
  • Step 2 – Water Goes Into the Bowl: Once the flapper is raised, water will start to fill up the toilet bowl. This water creates the pressure needed to push the liquid waste and solid waste through the S-bend and down into the waste pipe.
  • Step 3 – The Flapper Closes: As the toilet cistern water level drops, the flapper will close again, sealing up the exit hole. Now it’s time to refill the tank.
  • Step 4 – The Tank Fills: Because the water level is so low in the tank at this point, the float has dropped as well. This process opens up the fill valve, which is connected to your water supply. It releases water back into the tank through a small line that runs down the overflow tube.
  • Step 5 – Shutting Off the Valve: As the float reaches the previous water level, it closes the fill valve, shutting it off. Now, the toilet is ready for the next flush.

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