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Dual Flush Toilet: Definition & Technical Guide

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A dual flush toilet is a water-saving toilet that offers two flush options: a reduced-volume flush for liquid waste and a full-volume flush for solid waste. The reduced flush typically uses 0.8 to 1.1 gallons per flush (gpf), while the full flush uses 1.28 to 1.6 gpf. By giving users control over flush volume, dual flush toilets reduce average water consumption by 25 to 40 percent compared to single-flush models.

Canister Valve Mechanism, Washdown Bowl & Reduced Flush Volume Operation

Dual flush technology was developed in Australia in the 1980s as a response to chronic water scarcity and was standardized under Australian Standard AS1172.2 before spreading to Europe and eventually North America. The operating principle is straightforward: approximately 80 percent of toilet uses are liquid-only, so providing a lower-volume option for those uses saves significant water without sacrificing performance when a full flush is needed.

The flush mechanism in a dual flush toilet differs from a traditional flapper-based single-flush design. Most dual flush toilets use a valve-style flush mechanism — either a canister valve or a dual-button actuator connected to a valve — that lifts vertically to release water from the tank. The reduced flush lifts the valve partially, releasing a smaller volume. The full flush lifts the valve completely, releasing the full tank volume.

The bowl design also differs from standard toilets. Dual flush toilets typically use a washdown bowl geometry rather than the siphonic design common in American single-flush toilets. Washdown bowls use the force of the water falling from the tank to push waste through the trapway, while siphonic bowls rely on a siphon action to pull waste through. The washdown design works efficiently with less water but has a smaller water spot (the visible water surface in the bowl).

Button-Actuated, Lever-Actuated, One-Piece & Wall-Hung Configurations

Button-actuated dual flush toilets use two buttons on the top of the tank — a smaller button for the reduced flush and a larger button for the full flush. This is the most common dual flush configuration worldwide.

Lever-actuated dual flush toilets use a traditional-looking handle that actuates the reduced flush when pushed up and the full flush when pushed down, or vice versa. This design is familiar to American users accustomed to handle-flush toilets.

One-piece dual flush toilets integrate the tank and bowl into a single unit for a streamlined appearance and easier cleaning. These command a price premium over two-piece models.

Wall-hung dual flush toilets mount to a concealed carrier frame inside the wall, with the tank hidden behind the finished wall surface. Only the bowl and flush plate are visible, creating a modern aesthetic and simplifying floor cleaning.

Toilet Replacement, Low-Flow Upgrades & Rough-In Verification Services

Bonded Plumbworks’ plumbers install dual flush toilets as part of toilet services and low-flow fixture upgrades. In areas where water management districts encourage conservation, upgrading to dual flush models is one of the most effective single-fixture changes a homeowner can make.

Installation involves the same rough-in connections as any toilet replacement — a closet flange, water supply valve, and wax or waxless seal. Bonded Plumbworks verifies that the existing drain meets the minimum 3-inch diameter required and that the closet flange is at the correct height and distance from the wall for the new fixture’s rough-in dimension.

EPA WaterSense 1.28 gpf, ASME A112.19.2 & MaP Performance Testing

EPA WaterSense certification requires that dual flush toilets achieve a maximum effective flush volume of 1.28 gpf (calculated as the average of one full flush and two reduced flushes). ASME A112.19.2 establishes performance standards for toilet fixtures. MaP (Maximum Performance) testing rates flushing performance in grams of solid waste removed per flush.

TOTO Drake, Kohler Persuade, American Standard H2Option & Duravit Systems

TOTO produces the Drake and Aquia dual flush series with Tornado Flush technology. Kohler offers the Persuade and Veil dual flush models. American Standard manufactures the H2Option dual flush series. Duravit provides European-designed wall-hung dual flush systems.