If you've ever run your sleeping bag through a washing machine, you know the kind of damage it can do. Fortunately, a bathtub and some gentle hand washing is all you need to keep your bag performing efficiently.
Sleeping bags are more delicate than they look. Dirt, grime, and body oils can all build up to reduce their efficiency at insulating you when you need it. Plus, they can pick up odours that no amount of odor spray is going to help. Washing your bag in a conventional washing machine is a bad idea, since the agitator can mess up the insulation as well as tear up the delicate fabric. And while a front washer is gentler, many sleeping bags are just too bulky for them to handle.
Enter the bathtub. As Instructables user Boddeeen points out, that and some mild detergent is all you need. Fill your bathtub about halfway with warm water and add a small amount of gentle, powdered detergent. Turn the bag inside out, zip it closed, and put it in the tub to soak for about 15 minutes. Gently agitate the bag with your hands, drain the dirty water, and refill the tub with clean water. Lightly agitate again to get the soap out, let drain in the tub for about 15 minutes, and then gently move it to line dry. You want to be careful when agitating or moving the bag so you don't rip the shell or disturb the insulation too much. Hit up the post for full instructions and pictures.
How to Wash a Sleeping Bag [Instructables]