In recent years I've switched to the paper-towel type (Scotch blue seems best), so I don't keep the rags around anymore. It costs a bit more, to be sure, but it is safer, and I have a small metal trash can outside, with a plastic garbage bag inside like a liner, where I dispose of them until it is full. Then I take it to the curb with the garbage, and hope the trash truck picks it up and makes it to the dump before they combust...