My pair of Orvis Silver Labels recommend washing them in a machine using a mild detergent like Ivory Snow. Make sure not to use a liquid detergent. Check the label on your waders, it will probably give instructions, or you could check Orvis's website for care instructions.
I have washed mine multiple times, because I sweat a lot, and my waders get funky after several trips. After 7 years, I have to replace them.
Thanks to the LRO guys, I've already got my new waders. Simms Freestones. I hope these will last as long as the Orvis. Crawling and sliding over the rocks in the park are not easy on waders, but necessary, and kind of fun.