Miele PW 6163 Operating And Installation Instructions page 59

Optional modules
The ball valve must remain closed in normal operation. The ball valve
may only be opened during operation when necessary for taking
samples in accordance with the specified safety instructions.
There may be residual water in the hose system to the ball valve at
the end of the programme. Empty the hose system at regular intervals
to prevent the risk of germs and contamination.
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