<p>A vortex brake for a drain system has a vortex chamber with a curved peripheral side wall (29) surrounding a vortex axis in the vortex chamber, a central outlet (27) from the vortex chamber, a peripheral inlet (31) to the vortex chamber and a vent opening (41) in a wall of the vortex chamber. The vent opening communicates with a compression tank (45) outside the vortex chamber, into which compression tank air from the vortex chamber can be compressed.</p>
