Please follow the below steps for the best way to clean your dehumidifier:
Mix a solution of warm water, salt and/or vinegar and baking soda and pour into the small opening at the top of the tank. To avoid any mess, I would advise doing this in a sink or bathtub. Be sure to only fill the tank about a quarter of the way for it to be as effective as possible.
Once you've poured the solution in, give the water tank a vigorous shake as you won't be able to wipe or scrub at the inside to get the contents out.
Empty the tank of the solution and repeat. When finished, leave the water tank to dry in a cool, dry place. Once dry, it should then be sufficiently clean.
To prevent mold build-up, clean your dehumidifier like this once a week. Remember to remove any water in the tank when the dehumidifier is not in use.