A stopcock controls the flow of a liquid under pressure through a dispensing tube with an upstream portion separated by the stopcock from a downstream portion. The stopcock includes a housing portion with a chamber defined by a housing peripheral wall surrounding a longitudinal z-axis. The housing peripheral wall has an inner surface of revolution with a housing inlet opening connectable to the upstream portion of the dispensing tube. The stopcock includes an outlet connector connectable to the downstream portion of the dispensing tube and comprising an outlet opening. A plug defined by a plug outer peripheral wall snugly fitting the inner surface of revolution of the housing peripheral wall. The plug can rotate within the chamber about the longitudinal z-axis. The plug has a through-channel extending from an upstream opening located on the plug outer peripheral wall, to a downstream opening, such that the plug can be rotated about the longitudinal z-axis from a flow position to a sealed position, wherein, the plug outer peripheral wall comprises a seal protrusion topped by a ridge and forming a closed loop defining a blank area of the plug outer peripheral wall, such that, in the sealed position, the housing inlet opening of the housing peripheral wall faces the blank area and is circumscribed within the seal protrusion. The plug outer peripheral wall has a flow protrusion topped by a ridge circumscribing the upstream opening such that, in the flow position, the inlet opening of the cylindrical chamber peripheral wall is circumscribed by the flow protrusion, wherein said flow protrusion preferably shares a common portion of protrusion with the seal protrusion.