An auto-vented automatic stop flow pouring spout connectable to a container in order to pour with a rapid flow a non viscous liquid stored in said container with a minimum risk of accidental spillage and/or evaporation, said pouring spout comprising: - an inlet tube devised to be detachably connectable to the container for receiving the liquid stored therein; - an outlet tube slideably mounted externally onto the inlet tube for guiding the liquid from the inlet tube to a receiving container; - a liquid duct that is part of both of said inlet tube and outlet tube and through which the liquid stored in the container can flow; - an air duct that is also part of both of said inlet tube and outlet tube; - a valve system for simultaneously opening the liquid duct and the air duct when the outlet tube is slideably moved relative to the inlet tube; and - an internal spring to keep the inlet and outlet tubes in such a position with respect to each other as to keep the valve system closed unless a pressure is applied to the outlet tube in order to slideably move it relative to the inlet tube; said pouring spout being characterized in that: the valve system is devised so as to cause the liquid duct and the air duct to open separately into the storing container; and through the air duct air can come freely inside the container to considerably reduce vacuum formation within the container and allow faster liquid transfer through the liquid duct; wherein the valve system consists of a single piece of elongated form that is slideably mounted internally within the inlet tube, said piece having one end that is rigidly connected to the outlet tube so as to be moved with it relative to the inlet tube and that is divided into several longitudinal sections by means of radial walls so as to complete the liquid duct and the air duct of the outlet tube, said piece also having an opposite end shaped so as to act as a closing wall, said other end having a portion that is in line with the air duct and being of an angled hollow shape and provided with a narrow rectangular opening that permits a clear gradual opening of the air duct separately from the opening of the liquid duct when the piece is pushed by the outlet tube within the container in order to open it. - an inlet tube devised to be detachably connectable to the container for receiving the liquid stored therein; - an outlet tube slideably mounted externally onto the inlet tube for guiding the liquid from the inlet tube to a receiving container; - a liquid duct that is part of both of said inlet tube and outlet tube and through which the liquid stored in the container can flow; - an air duct that is also part of both of said inlet tube and outlet tube; - a valve system for simultaneously opening the liquid duct and the air duct when the outlet tube is slideably moved relative to the inlet tube; and - an internal spring to keep the inlet and outlet tubes in such a position with respect to each other as to keep the valve system closed unless a pressure is applied to the outlet tube in order to slideably move it relative to the inlet tube; the valve system is devised so as to cause the liquid duct and the air duct to open separately into the storing container; and through the air duct air can come freely inside the container to considerably reduce vacuum formation within the container and allow faster liquid transfer through the liquid duct; wherein the valve system consists of a single piece of elongated form that is slideably mounted internally within the inlet tube, said piece having one end that is rigidly connected to the outlet tube so as to be moved with it relative to the inlet tube and that is divided into several longitudinal sections by means of radial walls so as to complete the liquid duct and the air duct of the outlet tube, said piece also having an opposite end shaped so as to act as a closing wall, said other end having a portion that is in line with the air duct and being of an angled hollow shape and provided with a narrow rectangular opening that permits a clear gradual opening of the air duct separately from the opening of the liquid duct when the piece is pushed by the outlet tube within the container in order to open it.