Thrift Shop Towels?

So I need to make more liners for Pepper's cage. I have all the fleece bought, and normally I would use a towel as an inner absorbent layer, but I don't have any old ones lying around and even at "cheap" stores, towels are still like $10 each! Not horrid, except I need four of them, and their only purpose will be soaking up chinchilla pee....

I was thinking about seeing if I could get some towels from a thrift store, but I'd be worried about chemical buildup on them, if the previous owner had used a lot of scented detergents or dryer sheets or whatever with them..... at home we use eco-friendly scent free detergent on all our laundry, including the chinchilla stuff, but obviously I can't control what people did with their towels prior to my owning them.

Has anyone used thrift shop towels in their cage liners before? Is there anything in particular to do beforehand (other than just giving them a good wash) to make them safe(r)?

Thanks!!