A flushing trough is a long cistern which serves several WC

Flush toilet

A flush toilet is a toilet that disposes of human waste by using water to flush it through a drainpipe to another location. Flushing mechanisms are found more often on western toilets , but many squat toilets also are made for automated flushing...

 pans. It is designed to allow more frequent flushing.

Common uses

Flushing troughs are commonly used in places such as schools

School

A school is an institution designed for the teaching of students under the direction of teachers. Most countries have systems of formal education, which is commonly compulsory. In these systems, students progress through a series of schools...

, colleges

College

A college is an educational institution or a constituent part of an educational institution. Usage varies in English-speaking nations...

, public toilets, factories

Factory

A factory or manufacturing plant is an industrial building where laborers manufacture goods or supervise machines processing one product into another. Most modern factories have large warehouses or warehouse-like facilities that contain heavy equipment used for assembly line production...

 and public buildings where quick refill of the flushing cistern is required. Siphonic

Siphon

The word siphon is sometimes used to refer to a wide variety of devices that involve the flow of liquids through tubes. But in the English language today, the word siphon usually refers to a tube in an inverted U shape which causes a liquid to flow uphill, above the surface of the reservoir,...

 action is started in the same way as an ordinary flushing cistern and as the water

Water

Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

 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.