Placing a few drops of disinfectant in the water daily, such as Grapefruit Seed Extract (GSE), will prevent a buildup of bacteria in the tank of your humidifier. We add water to ours daily anyway so putting the GSE in the tank is a good idea. We also clean it out once a week.
I use about 15 to 20 drops GSE per gallon of water to wash off all the produce . I use a veggie brush and scrub, then let it sit for about a minute. Then I'll rinse and cut it up .It's not powerful enough to use as a bird cage disinfectant but it's good for the above cleaning tips. Nan