Drawstring backpacks are cheap and easy to use, although they don't carry as much as a normal backpack. They pull closed with drawstrings that double as your straps and they usually don't have any zippers. Drawstring backpacks are also usually made of nylon so they are easy to care for when they get soiled. While nylon is synthetic it can be machine washed and dried. Some drawstring backpacks might be made of canvas, which is another heavy duty material that can be machine washed.
Fill the washing machine with warm water if the fabric is nylon or another synthetic fabric, and cold water if the fabric is canvas or another natural fabric. Add the amount of detergent needed for the size of your load. If you have a front loading washer than this step will come after step 2.
Place the drawstring backpack in a lingerie bag with a zipper closure. This keeps the strings from wrapping around clothes while it washes. Zip the bag shut.
Place the lingerie bag with the drawstring backpack inside into the washing machine with like colors. Turn the washing machine to a normal cycle.
Remove the drawstring backpack in the lingerie bag from the washer when it's finished and place it in the dryer. Set the dryer to a warm or permanent press setting and turn it on. Keep the backpack in the lingerie bag.
Remove the drawstring backpack from the dryer when it's dry. Take the backpack out of the lingerie bag and shake the backpack out to remove any wrinkles.