Low-germ bottle venting.
The plugged in bottles can be shrink in follow of a vacuum. It is a normal process. Thats even good because it shows that the unit is airtight and germ-free is.

Because a high vacuum can lead to tearing of the bottles, we expressly point out in the dispenser manual instruction, to aerate the bottle manually.

Alternative we have the low-germ bottle venting ensures continually that the same quantity of air will be get into the bottle as liquid will taken and thus the bottles remain in their form. As a
result, the bottle will not tear and the liquid can not flow into the electronics unit.