Aha, a topic I'm somewhat familiar with ... smelly stuff.

Before washing, I have found that spraying the offending areas with a vinegar/water solution, or sometimes
just detergent & water, then a light scrubbing helps. Then I put the pack in a pillow case and tie off the top.
Washing the pack in the pillow case helps reduce straps, zippers, zipper ties, etc. from snagging on things.
Plus I can wash it with a load of other smelly bits and get more done. Air dry and it's good to go.

Edit: As FredOak mentioned, no really hot water. I wash everything cold/cold anyway to save $