I buy shop rags from the Auto parts store or Target. Usually get a bag of like 25 or so, for not a lot of $$. At the shop, we wash and reuse, cause we have a machine. But I would never wash rags in my own washer. Don't want that nastiness getting in my machine. Generally, at the shop, we throw them away when they are ratty w/ holes. At home, once it is full of dirt and grease.