i use dish washing detergent in warm water. what i do is this:
1: find a small bucket and fill it up with water
2: add dishwashing detergent and mix
3: submerge the whole filter in bucket and move it up & down
4: let it sit for like an hour
5: wash off detergent and use k&n filter recharge kit.
this is how i clean my filter ever since i had all that grease/dirt on it from driving without the fender lining.