The cistern that is attached to your toilet has undergone many changes over the last 15 years. The water supplied to the cistern is controlled by a float operated valve. Most of these valves are of a similar design to the ones used in the cold water cisterns. Prior to 1993, a 9 litre or 2 gallon flush was employed, having been like that for at least one hundred years, pretty much since the first toilet was designed. However, in order to try to conserve water the quantity was reduced, first to 7½ litres and then to a current maximum of 6 litres. In order to discharge this water from the cistern down into the toilet pan, a device is employed that closes when the required volume of water has been discharged. Toilet systems traditionally worked by using what is called a “Siphonic” device, however today there is another design which consists of a valve that is lifted allowing the water to flow as required. Archway Plumbers fit toilet systems.Below is a very brief description:Siphonic Action.This occurs when water is removed from a container without any kind of mechanical aid, travelling up and over a tube in a upside down ‘J’ shape. The long leg joins to the flush pipe whilst the short leg is open to the water inside the cistern. When the air is removed a partial vacuum occurs. This is triggered by a large diaphragm washer being lifted, discharging a quantity of water down through the flush pipe taking air and causing a partial vacuum.Valve Type.There are usually two buttons fitted to the cistern, one being for a short flush and one for a long flush. They work via a long and short rod system which will release small and bigger volumes of water as it is required. An Archway Plumber is familiar with this system.