I'm with Swampview on this one. The design of the K&N makes it so that MORE dirt actually filters better with no reduction in flow.

You should only need to clean it when it's basically coated with dirt. I "think" they say to hold a light to it and if you can still still the light, it's fine. Can't see the light, clean it.......

I check mine at every oil change, and have yet to see any dust making it past the filter.