A drinking receptacle comprising: a container for containing a fluid for drinking; and an outlet member having: an outlet through which the fluid is delivered under a pressure supplied by a user of the receptacle ; and a collar portion that attaches to an opening of the container such that an undersurface of the collar portion abuts with an upper surface of the opening of the container to form a sealed engagement between the outlet member and the container; wherein, both the undersurface of the collar portion and the upper surface of the opening of the container are formed from a rigid material such that the undersurface of the collar portion and the upper surface of the opening of the container are able to form a hard-to-hard surface engagement, and either the undersurface of the collar portion or the upper surface of the opening of the container that abut each other has at least one groove formed therein that extends across such abutting surfaces, the at least one groove having dimensions to ensure that the surface tension of the fluid at the at least one groove is maintained to reduce likelihood of fluid passing therethrough and further when said pressure is applied to the outlet member the at least one groove member forms a passage that permits the controlled ingress of air into the container to facilitate flow of fluid from the outlet, and when said pressure is removed the passage formed by the at least one groove member prevents the ingress of air into the container to facilitate a controlled vacuum pressure within the container , wherein the rigid material is a hard plastic material. a container for containing a fluid for drinking; and an outlet member having: an outlet through which the fluid is delivered under a pressure supplied by a user of the receptacle ; and a collar portion that attaches to an opening of the container such that an undersurface of the collar portion abuts with an upper surface of the opening of the container to form a sealed engagement between the outlet member and the container; wherein, both the undersurface of the collar portion and the upper surface of the opening of the container are formed from a rigid material such that the undersurface of the collar portion and the upper surface of the opening of the container are able to form a hard-to-hard surface engagement, and either the undersurface of the collar portion or the upper surface of the opening of the container that abut each other has at least one groove formed therein that extends across such abutting surfaces, the at least one groove having dimensions to ensure that the surface tension of the fluid at the at least one groove is maintained to reduce likelihood of fluid passing therethrough and further when said pressure is applied to the outlet member the at least one groove member forms a passage that permits the controlled ingress of air into the container to facilitate flow of fluid from the outlet, and when said pressure is removed the passage formed by the at least one groove member prevents the ingress of air into the container to facilitate a controlled vacuum pressure within the container , wherein the rigid material is a hard plastic material. <EOS>