I have a humidifier by walgreens it called a cool mist humidifier with a wicking filter the filter # is W899-WGN after taking it out can it be cleaned

https://www.walgreens.com/store/c/walgreens-humidifier-replacement-wick-filter/ID=prod6242355-product

How do I fill the tank with water

If there is a lot of scale and mineral deposits , you can run a 50/50 solution of White Vinegar and water thru it, by half filling the tank with the solution. When it's almost empty, turn it off, empty the remainder of the solution and flush the system with clear water. In the future I recommend that your use bottled Distilled Water, instead of tap water.

Either call or go back to the Walgreens where you purchased the Humidifier. They will either take one from another box or make a copy of it for you.

just warm water and bleach, will have to do it a couple of times

REPLACING THE FILTERS
Through normal use, waterborne minerals and sediment
become trapped in the wick filters. The harder your
water, the greater the amount of minerals in the water,
and the more often you will be able to monitor the life of
your filters in your humidifier.
You will be able to monitor the life of the filters in your
humidifier by checking the FilterCheck® Indicator. After
60 minutes of use, FilterCheck® Indicator will move and
indicate your filters condition. New filters will register in
the section reading Good filter. After frequent use of your
humidifier, the FilterCheck® Indicator will let you know
when the filters need to be changed, see Figure 2.
When the needle is in the CHANGE section, this means the
proper amount of moisture is not getting into your air due
to the excessive minerals and sediment that have become
trapped on your filters. At this point, you should replace your
filters. It is important to change your filters as
indicated to obtain stated performance level.
To replace the filter, follow the steps below:
1. Turn the unit off and disconnect from the electrical
outlet.
2. Remove the tank and main housing to access the base.
3. Remove the wick holder from the base of the humidifier.
4. Remove each individual wick and discard. Do not
remove rivet, replacement wicks come equipped with
rivets for easy replacement.
5. Follow the weekly cleaning instructions.
6. Insert new filters into each section of the wick holder
making sure the rivet attaches to the wick holder
securely.
7. Do not use wicks without rivets as this will not
produce the units intended output.
8. Replace the wick holder into the base and replace
main housing and then tank.
9. Repeat Operating Instructions.
It will take about 30 minutes for the humidifier to reach
maximum output.
Cheers!

http://www.jardenstore.com/manuals/MANUALS/HM1865-U_43_74701759.PDF

here is the website for the manual. when you download it go to the maintance section and it will let you know. if not. basically all you have to do is turn off your unit first. take the base and the tank off take out the wick filter disgard and put in new one. put everything back and turn on unit. and it should would like new

How long are you going between filter changes?

A filter that stops wicking water up and turns orange/yellow is one full of deposits.

It sounds like you have hard water. How are you filtering this water before you use it? Distilled water is the best.

Replace the filter. They don't last forever. Mine normally last a month to a month and a half.

Good Luck