Dual flush toilet


A dual-flush toilet is a variation of the flush toilet that uses two buttons or a handle mechanism to flush different amounts of water. A lesser amount of water is designed to flush liquid waste and the larger quantity of water designed to flush solid waste.
The system was developed by Japanese sanitary product manufacturer TOTO in 1960. It was equipped with two levers and built-in hand-washer, and was also revolutionary in that it reused the water in the hand-washer for flushing. However, it was not well known outside, or even within, Japan. In 1976, American industrial designer Victor Papanek proposed the dual flush system in his book Design for the real world, but the first practical implementation was designed in 1980, by staff at the Australian sanitary-ware company Caroma, with flush volumes of 11 and 5.5 litres. The design caught on, and a redesign in 1994 cut water usage to 6 and 3 litres.
The dual-flush toilet has become almost universally adopted in Australia, New Zealand, Singapore, and Israel, with its use in new buildings often mandated by legislation in those countries. The more complex dual-flush mechanism is more expensive than many other types of low-flush toilets.

Mechanism

;Push-button
Because it is a development of the traditional Australian flushing toilet, the push-button dual-flush toilet differs from siphon-flush toilets in that it relies on gravity to remove waste from the toilet. In addition to its dual-flush feature, the lack of siphoning also means that the toilet requires less water to operate. The lack of siphoning means that the waterline is considerably lower than that in siphon-flush toilets. The toilet has two buttons on the cistern rather than the single-flush one; one button delivers 3 litres and the other 6 litres. The lesser quantity is designed to flush liquid waste and the larger is designed to flush solid waste. It also uses a larger 10 cm trapway in the bowl, allowing for water to come out faster and clear the bowl efficiently.
;Lever
There are also dual-flush siphon toilets operated by a lever rather than buttons, with a 6l full flush, and a 3l half-flush if the flush handle is held down instead of being released immediately after flushing.

Advantages

The dual-flush toilet uses much less water. It was promoted by the Australian Government under its "Target 155" campaign. The first dual-flush toilets had a 4.5 litre and 9 litre flush, but innovations by Caroma brought that down to 3 litres and 4.5 litres respectively, achieving a WELS rating of 4 and 5 stars in Australia.
Australian governments have used rebates to encourage the replacement of old single-flush toilets with more water-efficient ones. For dual-flush toilets, with a star rating of 4 or higher, owners may be able to qualify to claim a rebate from the State Government in Victoria, New South Wales, or South Australia. Sydney Water's rebate program ended on 30 June 2011.
In Britain, the cost of a dual-flush mechanism which can be retro-fitted to an existing toilet was estimated to be from about £15 in 2007.

Disadvantages

While dual flush reduces running cost, the initial purchase price is higher, and replacing a toilet entails installation cost. In many cases it is possible to replace the flushing mechanism of an existing installation; such retrofitting can cost about US$30.
In the United States the National Energy Policy Act was signed into law in 1994, requiring that toilets sold use no more than 6 litres per flush.
Fixtures that use a maximum of 20% less than the federally mandated maximum of 6 litres receive the WaterSense label, a U.S. Environmental Protection Agency program designed to encourage water efficiency in the United States.
For dual-flush toilets to receive this label, the average flushing volume of two reduced flushes and one full flush must be below 4.8 litres.
While all dual-flush toilets are commonly seen as water-saving, some do not save as much as expected. In the US some dual-flush toilets have flushes of, although they do not fulfil criteria for the WaterSense label and cannot be classified as high-efficiency toilets.