I took the filter out of my Airsense 10, and it indeed did look a little grey-ish after 3 months nightly use. I blew it out with compressed air (laid it against a window screen to keep it flat) and then washed it out with warm water and liquid hand soap. After it dried, it looked like new. I will probably do that every 3 months or so, and get a new one after a year, since i don't get any freebies.
Yes, thanks Surferdude2 for the link
I think I will try that.
My machine is rented, so I think I will save the one bought filter I have left and stick it back in the machine when I return it or have problems.
The place I worked before had a HP 60" printer, and they had a warranty. But the warranty said you have to use genuine HP paper which was 3 times the cost of an off brand. When we had to call for service we replaced cheap paper with the one HP paper we kept just for that reason.
Same concept with my filter.