Take the filter out from the water tank (Note: you have to remove the water bucket first before you can remove the filter)
Mix equal parts of white vinegar and water in a container that is large enough to fit the humidification filter
Place the humidification filter in the vinegar-water container, making sure it is fully immersed. Soak for 1 hour
Discard the water-vinegar preparation
Rinse the filter under the tap until all vinegar residues is removed. Make sure to turn it in order to rinse both sides
Then drip off the excess water from the humidification filter and put it back into the water tank
Note: If your purifier belongs to the HU47xx, HU48xx or HU49 model series, then it's filter cannot be washed with vinegar. In this case, check the user manual for instructions.