I picked up a skein of Elefant Twist olefin fiber macrame cord (from the 1970s) at the thrift store in a bag of other crafting goodies. It was dirty and it smelled bad.
I knocked together a little crocheted basket in less than an hour. I melted the yarn ends to keep them from unraveling. Then I tossed it in the washing machine. No need to even drip dry – the spin cycle took care of all that. It looks (and smells) nice and clean.
I guess this is why rug makers like olefin so much!
I’m going to try washing the rest of the skein in a mesh bag so that I don’t have to handle it when it’s so dirty.