it's important to do everything you can to avoid having to wash you down or synthetic sleebin bag. use a liner, don't put it directly on the ground ever, don't go into it with bare skin ever, no peeing the bed, no sweaty sex, no shitting/cumming in there either, no snuggling with pets (specially dogs), no packing/storing the sleeping bag unless it's 100% dry (this means hanging it up to air-out/dry for at least a day or two after EVERY camping trip). dont' keep it in long-term storage without occasionally airing it out and fluffing it up to reloft the stuffing.
i don't know how to clean a bag because i do errthing to avoid having to :\