Method for avoiding the microbial attack of a cleaning apparatus for a metering unit, and cleaning apparatus

A liquid metering system comprising a plurality of containers arranged on a rotatable circular plate comprising a perimeter, each container operably connected to a metering unit arranged along the perimeter, wherein each metering unit is configured to receive a liquid from the container to which it is connected, and wherein each metering unit comprises a pump head configured, in a dispensing position, to dispense the liquid into a receiving container disposed below the rotatable circular plate;

• and wherein the rotatable circular plate is configured to rotate each metering unit between the dispensing position and a cleaning position;
• and at the cleaning position, a rotatable brush with bristles is disposed below the rotatable circular plate wherein the rotatable brush with bristles is configured to contact the pump head, wherein a gas comprising ozone is applied essentially radially to a plurality of bristles of the rotatable brush with bristles.