Found a link of on some cleaning tips of K&N Filter. Alternatively, you can go to K&N Homepage to know more about it.
1. Keep your stock paper filter and use it as a temporary replacement during cleaning
2. The top side of the filter element is what I call the clean side and the bottom the dirty side.
CLEANING
3. Liberally spray the cleaner in a brush stroke pattern along the ridges and valleys instead of across them. This allows the cleaner to get right into the tight nooks and crannies. Spray the dirty side first then from the clean side.
4. Leave it to for about 10 mins or so.
5. I found that if you also immerse it into a tub of cleaner solution. The type of biological cleaners and degreasers (the type used for cleaning kitchen grime). I immerse it for about 10 mins
6. Spray the filter from clean side first (note this can get kind of messy and dirty should you do it in the toilet so find a confined location). Spray along the valleys and ridges liberally until the water becomes almost clear. As most of the dirt is trapped on the dirty side you wanna flush most of it out.
7. Flip filter over and clean side. This is to flush out any dirt on the clean side. Flip it back and do a quick once over.
8. The filter should have a grey-white color and there will be some little traces of pink. Leave the filter on a newspaper with dirty side facing up in a dust free place to dry (avoid direct sunlight), best in aircon room overnight. Let it dry for about a day or 2.
OILING
9. From the dirty side, oil the ridges in a smooth consistent manner to ensure the oil is evenly spread
10 Leave the filter on some newpapers and some kitchen towels with dirty side up. The towels will soak up any excess oils.
11. Leave it for at least 30 mins
12. Hold it against a light source and check the pink color consistency. It okay to repeat 10-11 again.
13. Place your palm on the clean side for a few seconds and see if any oil is transferred. If so then you probably oiled it too much. Use a lint free rag and blot it dry. Try not use paper towel or tissue as they deposit fibres on the clean side.
Now you’re filter is ready for use.