These are what the manufacturers say:
http://www.uniflow.com.au/contents/en-us/d312.html
http://www.knfilters.com/faq.htm#18
...but they like to make money selling you their own 'cleaning' product.
Below is how i do it on DCOE Weber filter socks and it may not be perfect but its cheap and easy and how i was told to do it over 13years ago;
I use around 1lt of petrol (mower fuel usually) in a small clean container/bucket to wash the filter.
Remove the spring from the inside of the sock and then soak and massage the filter in the petrol till the oil, dirt and old fuel stains come out.
Youll see the dirt come to rest at the bottom of the container and the filter colour will slowly come back bright again.
Squeeze the filter dry by hand and empty the dirty fuel out of the container.
Then using a clean container put an approx mixture of fresh fuel and oil in at 20:1, (i.e.1lt of fuel and 50ml of engine oil).
Stir the oil and fuel together thoroughly in the container and then squish it through the filter gently by hand.
Ring out the filter again and let it dry in the shade completely.
The petrol will evaporate off and leave a fine film of oil through the filter to catch the dust.
Note: If you use too much oil it will clog the sock up at high revs and try to suck the sock into the carb.
If that happens use less oil in the fuel/oil mixture.
My filters have never deteriorated using this method despite what the manufacturers say.
Make up your own mind on how you want to do this. My way costs approx $3 in petrol and doesnt involve a trip to the shop to buy the 'cleaning kit'....