Take them to the carwash and use a pressure washer on them. You can use detergents in the pressure wash and then rinse with the pressure wash.
Alternately, soak in the bathtub with a nylon-safe bleach solution, then rinse very well.
While you CAN wash in a front-loading washer, every time you do so you take some of the fabric life.
I speak as a manufacturer of such equipment.
+1 car wash. Works for cats, too, by the way.
Hang it on the hitch ball of your truck or toss it in a large Rubbermaid bin. If you own a typical boat brush on an Adjustable pole it is nice for scrubbing between soap and rinse.I would have never thought of the car wash. I guess you can hang them on the things for the floor mats. Good idea, Thanks!
^^ someone has never had a really dirty pack.
If you are not happy with the results from dawn buy some 3m fabric protector and saturate the bag and let it soak for a while.It will soak into the fibers and lift all dirt and grime out when you wash it in the tub again and then retreat the pack so it will be easier should you need to wash it again.The instructions I read said no washing machine so I'd think the dishwasher would be just as bad if not worse. I'm going to try the bathtub method with some Dawn to see how that turns out. When it warms up outside I'll try the car wash method. Thanks for the tips.