Turn off and unplug your Vicks V400 humidifier.
Carry it to a sink. Lift the lid from the base. Turn it upside down and set it on your countertop.
Dump any water in the base down the sink drain.
Dampen a lint-free microfiber cloth in warm tap water and wipe the interior and exterior of your humidifier to remove any film or residues clinging to surfaces. Wipe the surfaces again with another damp cloth.
Refill the base and return the lid to its position. Plug in and turn on your humidifier.
Turn off and unplug your humidifier. Carry it to a sink. Remove the lid, turn it upside down and set it on your countertop.
Place your hand on the disk inside the lid. Twist the pickup tube gently toward "Off" to unlock it from the lid. Remove it and set it aside.
Dump any water in the base down the sink drain and then refill the base with 8 oz. of distilled, white vinegar. Put the tube in the base.
Wait five minutes, then clean the base and tube inside the vinegar with a lint-free microfiber cloth. Set the cloth aside, dump the vinegar down the drain and rinse the base and tube under warm, running tap water.
Add 1 tsp. bleach or hydrogen peroxide to 1 gallon of warm tap water in a jug or pitcher. Refill the base with this solution. Return the tube in the base.
Wait 10 minutes. While waiting, wipe the interior and exterior of the lid with a slightly damp cloth. Also, check the Dyna filter for debris and replace it if necessary.
Put on a pair of gloves and wipe the tube and the base interior thoroughly with the solution after the 10 minutes pass. Set the gloves and cloth aside and then wait another 10 minutes.
Dump the solution down the sink. Rinse the base and tube thoroughly under warm running tap water until you can no longer smell bleach, or approximately three minutes. Air-dry the pieces and reinsert the tube in the lid, then lock it in place to the "On" position.
Refill the base with water. Attach the lid and return your V400 to its original position. Plug in and turn on your humidifier.