English: A simplified diagram of a siphonic toilet cistern. The siphon is formed of a vertical pipe (1) that links the flush pipe (2) to a domed chamber (3). A perforated disc (4) covered by a flexible plate or flap (5) is joined by the siphon rod (6) to the flush lever. Pressing the lever raises the plate, forces water over the top of the siphon into the vertical pipe, and starts the siphonic discharge. Water flows past the flap until the cistern is empty, air enters the siphon and the flush stops.