A kink-resistant gas delivery tube configured to be directly connected to a circular male plug, the tube having an internal geometry of multiple concave and convex areas each having an apex, wherein an angle α between a tangent line to the apex of a concave area and a tangent line to a point of maximum slope between the apexes is 30 degrees or less, or wherein an angle β between a tangent line to the apex of a convex area and a tangent line to a point of maximum slope between the apexes is 30 degrees or less.
