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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. As the water is siphoned, the water level falls only inside a timing box designed to permit the required flush. When the timing box has been emptied of water, air enters through an air pipe to break the siphonic action. The timing box refills with water through a hole in its side. The cistern is then ready to flush.
The earliest example is from 1936. It was manufactured by Alisa and was intended to serve schools or places where toilets would be of high use. The cistern was made of cast iron and could serve 2, 3 or 4 toilets. 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. This was later adapted to hang over the back. A concealed variant was also available located in a 'duct' behind the wall to prevent vandalism. Maintenance could be carried out without entering the public space. A third version passes the chain through the cistern. The chain extended through a pipe higher than the water level and overflow level and thus no water would be splashed over the side while in use. Most flushing troughs had a longer life span than a standard single cistern. The main disadvantage is that maintenance requires all WCs served by the Trough to be unavailable.
Such troughs were used by local councils in the UK into the 1980s.