Dual Flush: #1 & #2
Dual-flush toilets can save water. The idea is that the controls provide just enough water to do the job, using a small volume of water for urine and possibly a little paper, and more water to flush away solid waste and ensure that the bowl is cleaned. They were common for several years in Europe before they started appearing in the U.S.
Below is a picture of a public toilet equipped with a dual-function handle, explained by an accompanying sign. The idea is that you lift the flush handle upward for a small-volume flush for liquid waste and push it down for a large-volume flush for solid waste (termed "#1" and "#2" just like in kindergarten).
A further innovation seen here is an anti-bacterial handle. The sign mentions that the flush handle is coated to protect against germs. The metal lever is covered with a green plastic coating which has been permeated with anti-baterial chemicals.
However, this example is a tankless model plumbed into a high-pressure high-flow supply, as typically found in public restrooms in medium to large buildings.
What about saving water with dual-flush technology in the home?
What about dual-flush technology for home toilets with tanks?
Dual-flush toilets are available, but you can convert an existing toilet to dual-flush operation.
Here are several conversion kits available through Amazon.
What you frequently find in European settings is a button on the top of the tank. Looking closer, you see that the button is split. Press the smaller segment to produce a smaller flush, press the larger segment and both parts move, producing a larger flush. Here are two examples from France.
These pictures show an American dual-flush system using nested buttons. Press down just the larger metallic area for a small flush, as seen in the first picture. Push down that plus the small inset blue plastic button for a large flush, as seen in the second picture.
This unit is at the Five Spot Loft hostel at 459 Myrtle Avenue in the Clinton Hill area of Brooklyn, just south of the Brooklyn Navy Yard.
Below is a sticker on the front face of a toilet tank explaining a dual-flush system.
As the sticker explains, this system complies with ASME A112.19.14.
The handle hangs down vertically. Push it to the left or clockwise for a 4.0 liter flush for liquid waste, or to the right or counter-clockwise for a 6.0 liter flush for solid waste.
The toilet seen here is at the Venice Beach Cotel along the boardwalk in Venice, California.
I removed the lid to photograph the mechanism.