I usually just toss the pieces once I've finished with them, as I haven't the patience to wash them. XD Terrible of me, I know, but I'm more comfortable starting out with a clean fresh piece straight from the bag than one that's been washed. Just a weird quirk I have.
The one time I did wash them, I soaked and rinsed in multiple changes of boiling water, until the cloth smelled clean, and line dried them in the bathroom. I need to go and buy a second package (it's very fine, good quality muslin.)