The spout can be used on a rigid or a nonrigid container. It includes a first member slidingly movable with reference to a second member so as to open and close a valve located at a front end of the spout. In use, the liquid flow can automatically be decreased and even stopped when the receptacle is full. The spout can include an annular outer gasket to create an airtight connection between the spout and the opening of the receptacle during pouring. This allows nonrigid containers to be emptied without collapsing. It also allows any airborne droplets and vapors present in the opening of the receptacle to be drawn into the container with the incoming air during pouring, thereby preventing or minimizing the presence of such droplets and vapors in the surrounding environment.