Gravity flush is the default residential toilet mechanism in the US. Water stored in the tank drops into the bowl via gravity (with the help of a flush valve at the bottom) when you press the handle, creating a siphonic flow that empties the bowl through the trapway. It's the engineering used in 95%+ of US residential toilets, including every major brand's volume models.
How gravity-flush actually works
The flush sequence:
- You press the handle → the trip lever lifts the flapper
- Water rushes from the tank through the now-open flush valve into the bowl
- The water raises the bowl water level above the trapway weir
- Water cascades into the trapway, creating siphonic action that empties the bowl
- Siphon breaks when air re-enters; refill cycle begins
Gravity-flush brand technologies
- TOTO G-Max — the original gravity flush, used on Drake series
- TOTO Double Cyclone — gravity + two angled nozzles for swirl cleansing (Drake II, Vespin II)
- TOTO Tornado Flush — gravity + three angled nozzles + larger valve (UltraMax II, Neorest)
- Kohler Class Five — gravity with 3.25" flush valve (Cimarron, Highline, Wellworth)
- Kohler AquaPiston — gravity with canister-style flush valve replacing flapper (Memoirs, Adair, Maxton)
- American Standard Champion 4 — gravity with 4-inch flush valve (Champion 4, Champion PRO)
- American Standard FloWise — gravity with refined bowl geometry (Cadet 3 FloWise, Edgemere)
- American Standard VorMax — gravity with circular water-distribution pattern (Heritage VorMax)
- Niagara Stealth Vacuum-Assist — gravity + vacuum dome above flush valve (Stealth Sabre, Liberty)
Gravity-flush advantages
- Simple mechanism, low cost
- No electrical or pressure requirements
- Universal aftermarket parts
- Plumber familiarity (every plumber services gravity-flush toilets daily)
- Long service life (25+ years)
Gravity-flush limitations
- Limited flush velocity vs pressure-assist
- 1.28–1.6 GPF is the practical floor for reliable flush performance (sub-1.0 GPF requires assistance — vacuum, pressure, or rimless engineering)
- Louder than tankless flush (the cascade of water is audible)