Siphon Jet
A siphon-jet toilet improves on basic gravity flushing by directing a focused stream of water (the siphon jet) straight into the trapway at the start of the flush. This jet rapidly fills the trap, creating a vacuum that ‘sucks’ the bowl contents out in one smooth motion. Because the siphon does most of the work, newer siphon-jet bowls achieve top MaP scores (up to 1 000 g) with as little as 1.28 gpf—or even 1.0 gpf—while remaining quieter than pressure-assist systems.
Concentrated water jet initiates a strong siphon for rapid bowl evacuation.
Typical high-efficiency rating: 1.28 gpf or less while maintaining 1 000 g MaP performance.
Quieter than pressure-assist; no internal pressure tank.
Fully glazed trapways and 3"+ flush valves boost reliability and reduce clogs.
Key Benefits
Powerful Flush Performance
The jet-induced siphon clears waste and paper in a single flush, even with lower water volumes.
- Achieves industry-leading MaP scores (up to 1 000 g).
- Reduces need for double-flushing and plunger use.
Water Efficiency
Modern siphon-jet toilets meet WaterSense 1.28 gpf limits—and ultra-high-efficiency 1.0 gpf models are becoming common.
- Saves up to 20 % more water than older 1.6 gpf gravity toilets.
- Qualifies for rebates in many municipalities.
Quiet & Comfortable
Gravity-assist plus jet action means no loud pressure tank noises or splashy turbulence.
- Smooth, quick bowl clearing without startling whooshes.
- Maintains a generous water spot for odor control.
How It Works
1
Flush Valve Opens
Pressing the handle lifts a 3"–4" flush valve, releasing tank water.
2
Jet Charges the Trapway
About 60–70 % of the water shoots through the siphon-jet nozzle at the bowl’s outlet, rapidly filling the trap.
3
Siphon Action Begins
Once the trapway is primed, a vacuum forms and pulls the bowl contents down the drain.
4
Rim Water Rinses the Bowl
Remaining tank water flows through rim holes, scrubbing the sides clean.
5
Siphon Breaks & Bowl Refills
Air enters the trapway, stopping the siphon. The fill valve restores tank and bowl water levels for the next use.
Who Needs This Feature
Homes Needing Extra Flush Power
Ideal where older plumbing, long drain runs, or frequent clogs require a stronger flush.
Water-Conscious Households
Combines high efficiency with reliable performance—no trade-off between saving water and clearing the bowl.
Light-Sleeper Bathrooms
Quieter operation makes late-night flushes less disruptive than pressure-assist options.
Commercial & Hospitality Settings
High MaP ratings reduce maintenance calls and keep restrooms presentable for guests.
Common Misconceptions
"Siphon-jet toilets use more water than gravity models."
Modern siphon-jet bowls are certified at 1.28 gpf or less, matching (or beating) standard gravity flush efficiency.
"They’re as loud as pressure-assist toilets."
Because they still rely on gravity, siphon-jet flushes are noticeably quieter—no compressed-air tank hissing or banging.
"The narrower trapway clogs more easily."
Fully glazed 2"+ trapways and the jet’s momentum actually reduce clog likelihood compared with many wash-down designs.
Frequently Asked Questions
Q: How is a siphon-jet toilet different from a basic gravity toilet?
A: A siphon-jet model directs most of the tank water through a jet at the bowl outlet, rapidly starting a siphon for a stronger, faster flush.
Q: Will a siphon-jet toilet work with low household water pressure?
A: Yes—the jet relies on tank head pressure, not supply line pressure, so performance is consistent even in low-pressure homes.
Q: Does the siphon jet need special maintenance?
A: Occasional cleaning of the jet orifice with a brush or vinegar soak prevents mineral buildup and keeps the flush strong.
Q: Are siphon-jet toilets available in dual-flush models?
A: Some manufacturers combine siphon-jet bowls with dual-flush valves, offering both low-volume and full-volume options.