Abstract: A tube system for propagating gaseous or liquid substances from a first tube (70) to a second tube (80) or vice versa includes a first connection (20) with a first connection element (40) which is to be contacted by the first tube (70) and a second connection (30) with a second connection element (60) which is to be contacted by the second tube (80). The outer diameter of the first connection element (40) is smaller than that of the second connection element (60). The inner diameter of the first tube (70) is slightly smaller than the outer diameter of the first connection element (40) and the inner diameter of the second tube (80) is slightly smaller than the outer diameter of the second connection element (60). Preferably, the first connection (20) also includes an outer diameter limiter (50), the inner diameter of the outer diameter limiter (50) being smaller than the outer diameter of the second tube (80) but larger than the outer diameter of the first tube (70).