Every modern toilet has two parts: the tank and the bowl. The tank is the upper portion that holds a reserve of water. The bowl is the lower part where you deposit liquid and solid waste to be whisked away down the sewer line. In part two of this two-part series about how your toilet works, we’ll explore the toilet bowl.
Toilet Bowl Parts
While the bowl isn’t as complex as the tank, it’s just as important. In fact, there are no moving parts in a toilet bowl, but the tank would be useless without it. The bowl accomplishes everything it needs to with just a few simple parts:
- Bowl: The lower bowl-shaped portion of a toilet.
- Rim holes: The openings around the edge through which water from the tank flows down the sides of the bowl.
- Jet hole: An opening near the bottom of some toilet bowls to increase the pressure of the flush and help decrease the chance of clogging.
- Outlet: The opening at the bottom of the bowl that leads to the trap.
- Trap: The area of plumbing immediately behind the bowl that curves downward and then upward to hold a constant pool of water.
- Siphon tube: The section of plumbing just beyond the trap that angles downward. Between flushes, the siphon tube remains empty.
- Sewer pipe: The plumbing line that connects to the bottom of the toilet. This is where waste and water flow when you flush the toilet.
The concept of a siphon or vacuum is what makes a toilet flush. When you press the handle, all the water rushes from the tank into the bowl through the rim holes/jet hole in about three seconds. This sends water flowing through the outlet and trap and into the siphon tube at a high enough rate to create a vacuum, causing water and waste in the bowl to be sucked out and down the sewer pipe. This results in the signature flushing sound you hear.
As soon as the tank empties and water stops rushing into the bowl, air fills the siphon tube, producing the distinctive gurgling sound as the siphoning process stops.
When the fill valve turns on the water to refill the tank, some of this water refills the bowl as well. A small flexible hose running through the overflow tube delivers water to the rim holes, where it runs down the sides of the bowl to refill the water lost when you flushed the toilet. It’s impossible for the fill valve to overfill an unclogged toilet bowl because the trap curves down into the siphon tube at the precise height the water should be in the bowl.
To test this, dump a cup of water into the toilet and notice that the water level doesn’t rise. You can pour cup after cup into the bowl, and it will never overflow because all excess water spills over the edge of the trap and drains away. If you pour in a bucket of water fast enough, you can replicate the siphon action caused by pressing the handle, meaning you can “flush” the toilet even with the water turned off.
Why Does a Toilet Overflow?
Of course, your toilet can overflow if the trap, siphon tube, or sewer pipe becomes clogged. In this case, the water has nowhere to go but up and over the rim. That’s when it’s time to break out the plunger!