Siphonic and Washdown Toilets
Courtesy of American Standard
Most siphonic toilets use gravity flushing.
You may think all toilets flush the same way, and maybe once upon a time that was true. But today toilets have several ways to wash away waste. These methods include:
Siphonic toilets use water to create a vacuum effect that pulls down waste. The siphonic method of flushing is the most common system in the United States, and siphon toilets traditionally come in two different styles:
• Gravity Flush: Most people are familiar with toilets that use the gravity flushing technique. When the flushing lever is pushed, a flapper in the tank opens and gravity forces water into the bowl. This triggers the siphoning action which flushes the waste down the trapway, which is the part of the toilet beneath the bowl where waste flows down and sewer gasses are prevented from entering your bathroom.
• Pressure-Assisted Flush: This method uses a flushing mechanism that combines water and pressurized air to flush the toilet. This combination of water and air pressure provides a stronger flush than gravity-flush toilets, but can also be nosier.
A toilet that uses the washdown method usually has a large trapway, typically around 4 inches, compared to the 2- to 3-inch traps of most siphonic toilets. Because the trap is so big, water cannot be siphoned; instead, water pushes the waste down through the trap.
Washdown vs. Siphon
- Washdown manufacturers like Caroma—an Australian company—produce toilets that employ dual-flush technology and work well with U.S. standards that require the maximum amount of water used to flush a toilet be 1.6 gallons per flush (gpf). American companies that make siphonic toilets are beginning to use dual-flush technology as well.
- Some siphonic toilets are susceptible to clogging, as 1.6 gpf may not generate enough water to dispose all of the waste. Clogging does not occur as much in many washdown toilets because they have a much bigger trap to dispose of waste.
- The drawback to washdown toilets is that waste is more likely to leave marks in your toilet bowl.