Flushing trough
A flushing trough is a long cistern which serves several WC pans. It is designed to allow more frequent flushing.
Common uses
Flushing troughs are commonly used in places such as schools, colleges, public toilets, factories and public buildings where quick refill of the flushing cistern is required. Siphonic action is started in the same way as an ordinary flushing cistern and as the water is siphoned, the water level falls only inside a timing box designed to permit the required flush only. Thus, when the timing box has been siphoned of water, air gets in through an air pipe to break the siphonic action. After a short period of time, the timing box refills with water through a hole in its side. The cistern is then ready for flushing again.
Background
The earliest example is from 1936 manufactured by Alisa and was intended to serve schools or places where WCs would be of high use. The cistern was made of cast iron and can serve 2, 3 or 4 WCs. To flush the cistern the chain that connects to the siphon is over the front of the cistern although water may sometimes slightly splash over the top so this was later adapted to hang over the back as the cistern's design was improved. A concealed variant was also available located in a 'duct' behind the wall to prevent vandalism and so maintenance could be carried out without interfering in the public space. A third version when the chain goes trough the cistern was also available where the chain would be extended trough a pipe higher than the water level and overflow level and thus no water would be splashed over the side while being used.
There is evidence of the cistern still being used by local councils into the 1980s where it was eventually discontinued although most Flushing Troughs have a longer life span than a standard single cistern the main disadvantage is that if maintenance is required all WCs served by the Trough will be unavailable. In some cases if there was 4 WCs, 2 Troughs could serve 2 WCs each.