I don't bother with it. I've also never had Sphagnum grow from spores in dried LFS. I've also never even seen any sporophytes, be it in dried LFS, in nature, or in culture. Only pictures.
Unless you're OCD about media, don't bother rinsing LFS. If you want live moss, don't waste your time hoping you get spores to germinate. Get some live moss, or trimmings, and grow it out yourself. It's pretty fast when it's in good conditions.