The device has a piping having a v or u-shaped and or generally arc-shaped first section running upward for an air supply line near a lower end which is connected to a second running part of a downward second section. From the second section a third perpendicular section branches upwards. From the highest point of the second part of the first section and the second section (5) of the piping a further bleeder tube (1) branches perpendicularly upward.
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