A pipe conveying molten material upwards from a pressurized receptacle into the mold of a low pressure diecasting machine, positioned on and supported by the receptacle, is secured in a fluid-tight fit by an adjustable coupling device. One end of the pipe extends through the topmost wall of the receptacle to pick up the molten material and the other terminates in a head located externally of the receptacle and tightened together with a seal against the mold. The outer surface of the pipe head has at least one substantially frusto conical portion matched to the surfaces of a plurality of wedges disposed circumferentially around the pipe and mounted on slide ways which can be directed by suitable actuators from an at-rest position to an operating position in which the pipe is subjected to an axial force with the pipe head clamped together with the seal against the machine.