A drinking container assembly comprising: a lid assembly comprising a lid housing having a top wall, a rim extending above, elevation-wise, the top wall and comprising an outer rim surface, an inner rim surface relative to a central section of the lid assembly, and at least one notch located on the inner rim surface, and a sidewall extending below, elevation-wise, the top wall and comprising an outer sidewall surface, an inner sidewall surface, relative to the central section of the lid assembly, and a lower sidewall edge; wherein said rim and said top wall define an upper portion and said sidewall and said top wall define a lower chamber portion; a drink opening and a vent opening; a flap rotatably coupled to the top wall and rotatable about a rotating axis, said flap comprising a body having a base portion, an extension having at least one locking lug projecting from an outer surface of the extension and engaging the at least one notch on the inner surface of the rim in a flap closed position to close the drink opening at the top wall, and a tab extending from an end of the extension, wherein the flap is rotatable from the closed position to an open position to expose the drink opening; wherein the side wall is coupled to an open end of a container, said container comprising a closed end; and Characterized in that: an opening is provided at the base portion of the flap; a gasket is secured to the opening of the flap and sealing the drink opening in the flap closed position; wherein the rim is a circumferential rim and surrounds the top wall and the rim having a rim edge; wherein the drink opening and the vent opening are located in the top wall such that the flap seals both the drink opening and the vent opening when the flap is in the flap closed position and opens both the drink opening and vent opening when the flap is in the flap open position. a lid assembly comprising a lid housing having a top wall, a rim extending above, elevation-wise, the top wall and comprising an outer rim surface, an inner rim surface relative to a central section of the lid assembly, and at least one notch located on the inner rim surface, and a sidewall extending below, elevation-wise, the top wall and comprising an outer sidewall surface, an inner sidewall surface, relative to the central section of the lid assembly, and a lower sidewall edge; wherein said rim and said top wall define an upper portion and said sidewall and said top wall define a lower chamber portion; a drink opening and a vent opening; a flap rotatably coupled to the top wall and rotatable about a rotating axis, said flap comprising a body having a base portion, an extension having at least one locking lug projecting from an outer surface of the extension and engaging the at least one notch on the inner surface of the rim in a flap closed position to close the drink opening at the top wall, and a tab extending from an end of the extension, wherein the flap is rotatable from the closed position to an open position to expose the drink opening; wherein the side wall is coupled to an open end of a container, said container comprising a closed end; and Characterized in that: an opening is provided at the base portion of the flap; a gasket is secured to the opening of the flap and sealing the drink opening in the flap closed position; wherein the rim is a circumferential rim and surrounds the top wall and the rim having a rim edge; wherein the drink opening and the vent opening are located in the top wall such that the flap seals both the drink opening and the vent opening when the flap is in the flap closed position and opens both the drink opening and vent opening when the flap is in the flap open position. an opening is provided at the base portion of the flap; a gasket is secured to the opening of the flap and sealing the drink opening in the flap closed position; wherein the rim is a circumferential rim and surrounds the top wall and the rim having a rim edge; wherein the drink opening and the vent opening are located in the top wall such that the flap seals both the drink opening and the vent opening when the flap is in the flap closed position and opens both the drink opening and vent opening when the flap is in the flap open position.