How to Wash a Sleeping Bag
Washing your bag in a bathtub

Spread your sleeping bag out on the bottom of the tub. Fill the tub about halfway with cool or lukewarm water, adding your mild soap. How much? Follow the directions on the label, but go easy on the soap—you’re going to have to rinse it all out again. Any soap that remains on your bag could breed bacteria and make it smell sour.
Use your hands (or your feet, if you want to channel your inner Lucy Ricardo) to agitate the bag in the water. If you see particularly stained or grubby areas, rub the fabric gently together in those spots. Let the bag soak for 20 minutes or so.
Drain the water from the tub, press (don’t wring) as much water as you can out of the bag, and refill the tub. Repeat this sequence a few times to rinse all the soap from the bag.
Once you’ve squished as much water out of the bag as possible, roll up the bag loosely and lift it into a laundry basket, so you can transport it to your dryer or to the laundromat.
You don’t want to haul the wet, heavy bag out of the tub and drape it over your arm to carry it—that could strain the stitching too much.
Washing your bag in a machine

If your washer has a “delicates” or “gentle” cycle, use that. If not, at least make sure the water temperature is cold or (at most) warm.
Add your mild soap, following the directions on the label.
Once the washing cycle is done, repeat just a rinse cycle, if your machine gives you this option. If you can’t do that, run the bag through the regular cycle again, but don’t add any soap.
Remove the bag from the machine very carefully (watch those stitches!), and transfer it to your dryer.