Fill the humidifier tank with water. Add 1 tbsp. of bleach to the tank. Let the tank sit for 30 minutes. Do not run the humidifier with bleach inside the tank.
Remove the filter and put it into a large saucepan with water and 2 cups of vinegar. Let it sit for 30 minutes.
Fill the base of the humidifier with undiluted white vinegar and let it sit for 30 minutes. The amount needed will depend on the size of your base. Pour the vinegar out and wipe the base with a soft cloth, removing any residue.
Pour 1 tsp. of bleach in the base for every gallon of water and let sit for 30 minutes.
Rinse the tank and base thoroughly, removing any hint of bleach. Reassemble the humidifier and fill it with clean water.