Unplug the dehumidifier.
Open the access panel on the side of the dehumidifier to pull out the filter inside the machine.
Mix 1 tbsp. of mild liquid dishwashing detergent with 1 gallon of warm water. Dip a soft cloth in the solution and use it to wash the filter.
Rinse the filter clean with warm running water.
Allow the filter to air dry completely.
Replace the filter and close the access panel.
Plug the dehumidifier back in.