Siphonic flush valve for toilets

A siphonic flush valve for a toilet, said toilet having a toilet tank and a toilet bowl, said siphonic flush valve comprising a housing supportable in said toilet tank and defining a chamber, an upleg open to said chamber and a downleg open to said upleg, said chamber including a manually actuatable piston means slideably supported therein for forcing water in said chamber into said upleg at the start of a flush cycle, said chamber further including a collar defining an opening, and a check valve movably supported in said opening, the height of said check valve being manually adjustable in said opening to control the siphonc flush action of said flush valve, said check valve includes a movable member which closes said check valve when said piston means is manually actuated to force water in said chamber, said check valve being frictionally supported in said collar to allow slidable manual adjustment of the height of said check valve, said piston including openings therein to allow water to flow therethrough.