I know that may sound crazy to some people, but I worked in some shops that had a cleaning service come in to wash not only all of the uniforms every week, but the used rags also. I know it's common practice. Even the greasiest, most oil soaked, dirt embedded, used to wipe grease from the concrete floor- you get the idea. I'm wondering what type of detergent they use. The rags would come back perfectly clean every week. Now, obviously the home mechanic would not want to use his regualr washing machine to wash rags...unless he wants to get in REALLY deep [censored] with his wife. But maybe it would be cost effective in the LONG run to have a dedicated, cheap washing machine for coveralls and rags. We all know many rags get used when greasing trucks and heavy equipment...