Is there any way of cleaning a hepa filter? I have an astronomically expensive vacuum with an equally expensive filter which is perhaps an inch thick. It has developed a black layer, possibly a tenth of a millimeter thin on the underside, which I suppose is all the microscopic particles it is supposed to have stopped being thrown out into the atmosphere. I have a strong suspicion that if I can get it off I can use the filter at almost maximum efficiency for a while longer before I have to replace it.
Can it be scraped off effectively or put in a dishwasher like sponges sometimes need before you chuck them away? Or brushed with baking soda or something like that?
Or will just cleaning it with warm or boiling water do a reasonable job?