An accessory for a drinking vessel is disclosed as including a body (102) with a passageway allowing air or liquid to pass through, the body including a first wall (104a) and a second wall (104b) which are opposite to each other, and a valve (110) in the passageway, the valve (110) including a first valve member (110a) and a second valve member (110b), in which both the first and second valve members (110a, 110b) are integrally formed with the first and second walls, and each of the first and second valve members (110a, 110b) includes respectively a first surface (111a, 111c) and a second surface (111b, 111d) which are opposite to each other, in which the first surfaces of the first and second valve members face generally a first direction, and the second surfaces of the first and second valve members face generally a second direction which is opposite to the first direction, and the first valve member is deformable between a first configuration in which at least part of the second surface of the first valve member contacts and overlaps at least part of the first surface of the second valve member to prevent flow of air or liquid through the valve and a second configuration in which the first valve member is out of contact with the second valve d member to allow flow of air or liquid through the valve.
