A syphon assembly (1 fig 1) for discharging water from a cistern. The assembly includes an inverted, generally U shaped duct (2 fig 1), an open-ended chamber (3 fig 1) and a piston (4 fig 1) movable in the chamber to which a flexible diaphragm 50, 51 is mounted for initiating a syphonic action. The duct includes an upleg (20 fig 1) and a downleg (21 fig 1) and the chamber is fluidly connected to the upleg. The assembly includes a constraining means 52, 53, 54, (35 fig 2) that is configured to constrain at least a peripheral portion of the diaphragm such that it deforms in a substantially predetermined manner. A further embodiment relates to a syphon assembly comprising a diaphragm with a hinged portion. A further embodiment relates to a syphon assembly wherein a valve means comprises two pivotable flaps. A further embodiment relates to a syphon assembly comprising a diaphragm that abuts against a buttress means. A further embodiment relates to a syphon piston comprising a cross member and a plurality of beams extending between the cross member and a peripheral portion of the piston.
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