Around 1980 Australian engineer Bruce Thompson of Caroma Industries in South Australia patented a particular two-button dual- flush toilet cistern, that today is a standard feature of many bathrooms around Australia.
The dual flush has the primary function of varying the volume of water discharged during flushing.
The accompanying diagram shows Caromas patented system.
The cistern includes two reservoirs A and B and a valve C. By depressing either button D or E respective shafts F and G engage third shaft H which lifts valve C emptying either reservoir A and/or B. However, when depressing button D shaft F also engages arm L which rotates hinged stopper K to seal off reservoir A allowing only reservoir B to empty creating the reduced water flow.
At the time, the Caroma dual-flush cistern was so revolutionary that the shape of the toilet bowl had to be redesigned to accommodate the reduced water flow to ensure the toilet worked correctly. Over the past 20 years the Caroma dual-flush cistern (and other similar dual-flush mechanisms) have saved Australian households hundreds of thousands of litres of water and been so successful that legislation throughout Australia changed to encourage their use.