You're talking about the accordian type? Blow it out with an air hose. It's not a very good filter. It looks cool, but it allows micro particles to get through.
Go with a Motor Saver air filter. They're the best you can get.
I didn't think that they could be cleaned. I thought they were disposable (replaceable), that's why they are so cheap. You can usually get several of them for only a couple of bucks.
Be careful w/ an air hose, if you use too much pressure you can tear the paper. Hopefully, someone else will have an answer for you.