Toilet Flush Type Guide: Gravity, Dual, Pressure Assist

Every toilet clears the bowl using one of three meaningful flush mechanisms: gravity, pressure-assisted or dual-flush. Everything else you see on spec sheets (Double Cyclone, Tornado Flush, G-Max, Class Five, AquaPiston, Flushmate) is a branded variation inside one of those three families. Understanding the family first, then the variation, is the fastest way to buy correctly. The mechanism controls four things you cannot change after installation: how many grams of solid waste a single flush clears, how many gallons that takes, how loud the toilet is and how much it costs to repair when a part fails. This guide works through each mechanism with published data, explains the branded sub-types, answers the questions search engines surface most, and pairs each section with specific model recommendations so you can act on the information right away. For the broadest cross-type comparison of outright flush power, the pillar guide to the best flushing toilets ranks them side by side.

Choosing a flush type is also connected to choices about bowl shape, seat height and one-piece versus two-piece construction, since those physical decisions affect which flush mechanism fits a given bathroom. The complete 2026 guide on how to choose a toilet covers those dimensions in full. This page stays tightly focused on the mechanism itself.

What is a gravity flush toilet, and how does it work?

Press the lever on a gravity toilet and a flush valve (usually a flapper or a canister) opens at the bottom of the tank. Water drops by gravity into the bowl. When the volume raises the standing water past the top of the internal trapway bend, a siphon starts: water rushing over the crest pulls everything in the bowl after it in a sustained, low-pressure suction. Air breaks the siphon when the bowl empties, the flapper closes, and the fill valve refills the tank. The entire sequence uses household water line pressure of around 25 to 80 PSI only to fill the tank slowly between flushes. The flush itself is powered by nothing but water weight and bowl geometry.

Flush strength in a gravity toilet comes from how quickly and completely the tank empties and from how well the bowl shape initiates the siphon. Older 2-inch flush valves released water slowly, which is why early low-flow toilets earned a reputation for weak clearing in the 1990s. Modern designs use 3-inch or 4-inch valves that dump the tank in a fast surge, paired with computer-optimized bowl profiles that start the siphon almost instantly. The TOTO Drake II uses a 3-inch valve and a Double Cyclone jet to hit a 1,000-gram MaP score on 1.28 gallons. The American Standard Champion 4 uses a massive 4-inch valve and a 2.375-inch glazed trapway to move bulk that narrower designs sometimes cannot. Understanding which valve size a toilet uses tells you more about real-world flush quality than most of the marketing text on the box.

What is a pressure-assisted toilet, and who should buy one?

The vessel inside a pressure-assisted toilet (most commonly a Flushmate cartridge, widely used in Gerber and American Standard pressure-assist lines) works like a small pneumatic tank. Line water pressure, typically 25 PSI minimum and ideally 45 to 80 PSI, compresses trapped air as the water fills the vessel. When the trip lever releases the valve, that compressed air pushes the full water charge into the bowl at a velocity that gravity alone cannot match. The result is a loud, fast, powerful flush with very little residue left in the bowl.

The trade-offs are significant. Pressure-assisted toilets are distinctly louder than any gravity design, often producing a sharp bang-whoosh that carries through walls. The sealed Flushmate vessel costs $80 to $200 to replace and usually requires the entire cartridge to be swapped when it fails, compared to a $5 flapper on a gravity toilet. They also require adequate incoming water pressure, typically 25 PSI minimum, and can be problematic in homes or buildings with low line pressure. For a well-matched use case, such as a busy office restroom or a household where clogs are a recurring problem, the power is worth these concessions. For a quiet residential master bath or a home near a sleeper's bedroom, a top gravity model reaches the same MaP score while staying silent.

What is a dual-flush toilet, and is it worth it?

Dual-flush is best understood as a smarter water-delivery strategy layered on top of a gravity or washdown bowl rather than a separate mechanism entirely. The tank contains a two-stage tower valve connected to a split push button or a split lever. Pressing the smaller button releases a partial charge of water for a rinse flush. Pressing the larger button opens the full valve for a complete solids flush. The technology has been available for decades, is dominant in Europe and Australia, and has grown steadily in the United States as water rates rise and EPA WaterSense standards tighten.

The water savings are real, but they depend on household behavior. A family that consistently uses the small flush for liquids can cut toilet water use by 20 to 30 percent versus a fixed 1.28 GPF single-flush. The honest limitation is that many dual-flush bowls use a washdown action rather than a deep North American siphon, which can result in more skid marks on the bowl and occasional need for a brush. The two-stage valve also has more moving parts than a single flapper. For buyers motivated by long-term water savings or green building certification, the format is hard to beat. The complete toilet buying guide for 2026 covers the full cost-benefit calculation for dual-flush in more depth.

Siphonic vs washdown: what is the real difference?

Almost every toilet sold in North America is siphonic. The TOTO Drake, Drake II and UltraMax II, the Kohler Highline, Cimarron and Santa Rosa, the American Standard Cadet 3 and the Gerber Viper are all siphonic gravity designs. The narrow trapway on a siphonic toilet fills completely during the flush, at which point air can no longer enter from the drain side, and suction takes over to pull the waste down. This produces the characteristic "whoosh" and gurgle of a North American toilet. Because suction, not just water velocity, does the clearing, siphonic toilets can clear waste efficiently on relatively low water volumes, which is why 1.28 GPF WaterSense siphonic models perform well.

Washdown toilets use a wider, shorter and straighter trapway, typically 4 inches in diameter, that pushes waste straight down without building suction. Because the trapway does not need to fill completely to function, it can be much wider and therefore less prone to physical obstruction. The tradeoff is a smaller water surface in the bowl, which means more visible residue and a greater need for the brush, plus a louder and less elegant-feeling flush to many North American users. The Swiss Madison St. Tropez and the Woodbridge T-0001 are among the dual-flush washdown designs popular in the U.S. market. The one-piece vs two-piece comparison covers how washdown bowls often tie to one-piece construction, since the shorter trapway suits the lower profile of a one-piece frame.

What do "Double Cyclone," "Tornado Flush," "G-Max," "Class Five" and "AquaPiston" actually mean?

These are manufacturer brand names for engineering refinements within the gravity siphonic family, not separate flush categories. Understanding what each one is prevents marketing language from obscuring a simple comparison.

TOTO G-Max: TOTO's original high-power siphon system, used on the TOTO Drake. Uses a large siphon jet and a wide glazed trapway. Reaches 1,000 grams on 1.28 GPF. TOTO Double Cyclone / Tornado Flush: TOTO's refined system, used on the Drake II, UltraMax II and Vespin II. Replaces the single jet with two or three angled nozzles in the rim that create a centrifugal water swirl inside the bowl, scrubbing the surface more completely before the siphon starts. Also reaches 1,000 grams on 1.28 GPF with a quieter, cleaner rinse. TOTO Dynamax: The newest TOTO siphon system, optimized for even faster tank evacuation. Kohler Class Five / AquaPiston: Kohler's canister valve system, which opens 360 degrees (versus a flapper that lifts from one hinge point), releasing water from all sides of the valve opening simultaneously for a faster, more even tank dump. Used on the Highline, Cimarron and Santa Rosa. American Standard Champion 4: Not a branded flush system but a product line named for its 4-inch flush valve, the largest common flush valve in residential gravity toilets. Pairs that large valve with a 2.375-inch trapway for maximum bulk-pass capability. Woodbridge T-0001/T-0019 and Gerber Viper/Avalanche: Standard siphonic gravity systems (Viper) and pressure-assisted (Avalanche) without unique branded flush names, compared on MaP scores and trapway specs directly.

The takeaway is that when you see any of these names, you are still buying a gravity siphonic toilet. Compare them on published MaP grams, GPF and trapway width, because those numbers cross all brands without translation.

Which toilet flush type has the strongest flush?

MaP (Maximum Performance) testing is the only third-party, independently published measurement of how many grams of solid waste a toilet clears in a single flush. The residential pass threshold is 350 grams. A score of 800 grams is very good. A score of 1,000 grams is the top of the published range, and multiple toilets across gravity and pressure-assisted categories reach it. The score is the most reliable predictor of real-world flush strength because it is measured with a standardized soybean-paste media under controlled conditions, not through marketing copy. Every product recommendation in this guide is accompanied by its published MaP score. If a toilet's MaP score is not publicly listed, treat that as a meaningful warning: most strong performers publish the number because it helps them sell.

Raw force is not the only dimension of flush quality. A toilet that clears 1,000 grams but leaves skid marks, takes 30 seconds to refill or makes noise that wakes the house is not necessarily the right choice. Match MaP score to noise tolerance and repair cost for the complete picture. The round vs elongated toilet comparison also touches on how bowl shape affects where the flush jet contacts the bowl, which influences cleaning efficiency even at the same MaP score.

What is the best flush type for preventing clogs?

Clog resistance comes from two things the flush type and bowl design control directly: how much kinetic energy reaches the trapway at the moment of flushing, and how wide and smooth that trapway is. A wide trapway simply passes larger objects; a glazed trapway (like TOTO's CeFiONtect ceramic glaze or American Standard's EverClean surface) prevents partial waste adhesion that builds up over time and gradually narrows the effective passage. Pressure-assisted wins on energy, since the air-propelled water charge never weakens as a flapper does. Among gravity toilets, the Champion 4's 2.375-inch trapway leads the field, but TOTO's 2.125-inch fully glazed CeFiONtect trapway on the Drake II is nearly as effective and considerably quieter.

A high MaP score is the best single predictor of clog resistance, because the test measures exactly the clearance scenario a clog represents. A toilet with a 1,000-gram score is unlikely to clog on normal household waste. Toilets with scores below 600 grams are more vulnerable. If your household has had recurring clog problems, check the MaP score and trapway specs before buying any replacement, regardless of the brand or the price.

Which toilet flush type is the most water-efficient?

EPA WaterSense is the federal efficiency certification that matters for rebates, green building credits and water utility incentives. A WaterSense toilet must flush at 1.28 GPF or less (single-flush) or average below 1.28 GPF on a weighted basis (dual-flush, where the calculation is 0.5x full-flush GPF plus 0.5x reduced-flush GPF). Most TOTO, Kohler and American Standard gravity models currently on the market carry WaterSense certification. The TOTO Aquia IV at 0.8 / 1.28 GPF, the Woodbridge T-0019 at 0.8 / 1.6 GPF and the Swiss Madison St. Tropez at 0.8 / 1.1 GPF all carry the label. Among single-flush gravity toilets, the 1.28 GPF models from TOTO, Kohler and Gerber are WaterSense certified and use roughly 20 percent less water per flush than a legacy 1.6 GPF design.

Best Gravity Flush

TOTO Drake II

Best for most homes

4.8

1,000-gram MaP on 1.28 gallons through a quiet Double Cyclone siphon, with a fully glazed CeFiONtect trapway and cheap, widely available parts.

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Best Pressure-Assisted

Gerber Avalanche

Best for heavy traffic

4.4

Flushmate compressed-air vessel delivers a forceful 1,000-gram blast that never weakens with use, suited to commercial or multi-family bathrooms where a clog is not acceptable.

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Best Dual-Flush

TOTO Aquia IV

Best for water savings

4.6

0.8 / 1.28 GPF dual-flush with an 800-gram full-flush MaP score, WaterSense certified, and TOTO's skirted one-piece design that makes cleaning easier than most dual-flush alternatives.

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1. How often is the toilet used, and by how many people?

Usage intensity is the most important factor that most buyers underweight. A toilet used by one or two people in a quiet home has different demands than one used by a family of six or a multi-occupant rental unit. Gravity siphonic toilets handle normal residential use, meaning 8 to 30 flushes per day, reliably for 10 to 20 years with standard part replacements. Pressure-assisted toilets are built for heavier cycles without weakening: the compressed air charge is identical on flush 5 and flush 500, whereas a gravity flapper gradually loses its seal and a worn fill valve fills slower. For a bathroom that functions like a light commercial fixture, the pressure-assisted option earns its higher repair cost. For typical home use, gravity's cheap maintenance wins clearly.

2. How important is noise?

Pressure-assisted toilets produce a loud, forceful "whoosh" that is audible through closed doors and commonly described as startling in a quiet house at night. A top gravity siphonic toilet like the TOTO Drake II or UltraMax II is nearly silent by comparison: the Double Cyclone siphon produces a low hum and brief gurgle that is far less intrusive. If the toilet is near a bedroom, in an open-plan home or in any setting where noise matters, gravity is the only sensible choice. Dual-flush toilets using a washdown mechanism fall in between: the reduced flush is very quiet, the full flush slightly louder than a siphon because there is no sustained siphon suction to muffle the water exit.

3. How important are water savings?

If a lower water bill or a green building certification is a primary driver, dual-flush is the logical target. A household averaging 22 flushes per day that shifts to a 0.8 / 1.28 dual-flush model and uses the small flush 70 percent of the time will average approximately 0.94 GPF, compared to 1.28 GPF for a WaterSense single-flush toilet. That is a saving of about 7.5 gallons per day per toilet. Over a year and across two bathrooms, the savings exceed 5,400 gallons per toilet, enough to matter on a metered water bill in a high-rate market. For buyers who primarily want to hit WaterSense certification without the dual-flush complexity, any 1.28 GPF gravity model achieves the label at a lower price and with simpler parts.

4. How much do repair costs matter over 10 years?

Total cost of ownership over a decade looks very different across flush types. A gravity toilet's expected repair parts are a fill valve ($10 to $25), a flapper ($4 to $12) and occasionally a flush handle ($8 to $20), all available in any hardware store and installable by a non-plumber in under 30 minutes. A dual-flush toilet's tower valve costs $15 to $50 to replace and requires slightly more technical disassembly. A pressure-assisted Flushmate vessel costs $80 to $200 to replace and may require a plumber if the water line fittings are not accessible. Over 10 years in a normal home, the gravity toilet often has a lower total cost of ownership even if its purchase price is similar to the alternatives. The decision changes in a high-use commercial setting where the Flushmate's longevity under heavy cycling offsets its higher replacement cost.