I assume your talking about the HD filter system? There are two types - one you oil (obsolete) and the other dry. This is just about the dry version (last 10 years).
First, keep your pre-filter clean regularly by just banging it out or washing (I leave mine in my jeans pockets to "fool" the wife) and if it doesn't fit tight, chuck it and buy another - $4-$5 I have a couple of spares so I can just snap one of and the other rather then mess around while I'm milling.
The main filter cartridge is just dunked in hot soapy water for a few minutes (I spray mine with dilute purple cleaner) and then run the garden hose though them INSIDE to OUT). Blow out with air if you have it.
If you have a tight pre-filter (no curling edges, elastic in good shape), and you knock it clean by bashing it on something hard, little gets though to the main filter. If your saws is spitting back a lot of gas into the filter, the oils and resins from the wood will harden and block. Purple cleaner is a good solution. Make sure your inner sponge is in place to trap any spit-back, or if a later saw, the defector is installed.
Eventually you'll get some buildup between the outer Stainless mesh and the fleece. It's hard to get out but I've taken some really bad dry HD filters from the garbage can, ultrasonically cleaner them for about 30 minutes in purple cleaner, and washed them out. 90% are still in use...
