What Does the Siphon Jet in a Toilet Do?


Toilets have come a long way since the lowly outhouse. A variety of flush-improving toliet technology have been developed to ensure the average user gets the most out of an ever-decreasing flush size. The siphon jet is another technological leap in toiletry, helping to increase the power of a flush without increasing its water volume.

The Basic Flush

  • A toilet bowl is designed with an air pocket in the bend that enables the formation of a vacuum. When you push the handle on the toilet tank, a valve releases the water held in the tank into the bowl. This action overcomes gravity and the toilet's nature to hold water in the bowl by creating a vacuum that sucks the contents of the bowl down into the drain.

The Tiny Flush

  • Old-fashioned water-wasting toilets have a 5 gallon flush. The sheer volume of water rushing into the bowl forces anything and everything down the drain. Since water conservation efforts began in the 1980s, the standard flush has dropped considerably. The early 1.6 gallon flush models were often inefficient at removing solid waste and toilet paper, prompting the improvement of the flush.

Enter the Siphon Jet

  • The siphon jet is a molded pocket in the front of the toilet that holds extra water until a flush is initiated. It points directly into the trapway. When the toilet flushes, the vacuum action pulls the stored water out of this pocket, increasing the pressure of the flush. It is a feature found on many, but not all toilets.

Siphon Jets Tested

  • The University of Washington tested a variety of siphon jet toilets before replacing 2,000 of their older style toilets with more efficient toilets. Among the tests was an examination of the amount of toilet paper each toilet could flush at one time. In this test at 25 psi, the Toto toilet outperformed all the others, flushing an impressive 40 feet of paper. The runners-up were toilets by Kohler and Crane. Overall, however, Crane led the pack on other study tests, followed closely by Toto and then Kohler.

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