Cleaning a K&N air filter for re-use.....
Get a small air filter size bucket... dump two scoops of Oxy powder in it. Then place the air filter in there..... pour 1 1/2 2 liter bottles of generic club soda in the bucket.....about 3 litres total...depending on the bucket you use...a smaller bucket uses less club soda etc...

It bubbles and foams up almost Instantly as a greasy dirty film and tons of dirt and crap jumps out of the filter gauze. The foam's all topped with yellow filter oil & dirt, grime and bug stuff...it's amazing that all that stuff was still in there after having cleaned the filter three times the "normal" way. The club soda is the trick. The carbonation 'boils' the crap out of the filter's gauze fibers instantly.

Use a piece of paper to scoop out the nasty oily grime & dirt that's riding on top of the foam in the bucket and toss the paper away so you don't have to lift the filter up/out thru that stuff.... swirl the filter around in the solution for about 3-4 minutes and let it sit for a minute or so.....finally shake it in the solution for a few seconds and pull it out...elapsed time about 10 minutes.

This is much better than blasting it with water trying to rinse the crap out or blowing it out with an air hose.

let it dry really good, oil the filter up and reinstall it.... some people have two filters so they can keep one oiled, clean, and plastic bagged, do a speed swap and then take their time cleaning, drying and oiling up the other one.-Bob