Dawn platinum scrub and then maybe additional one adding Borax to the soap? Borax is a known thing you add to wash to help get out the smells. I always add that to my hunting gear wash.
Also get an Ozone generator device. I've got a nicer sized one I can set to run for a certain amount of time. Just shove it into the pack and let that ozone break down that organic matter particles that's left behind. Also those sprays for Cat and Dog Urine/feces accidents will help tool. They are Enzymatic cleaners that work by helping to naturally breakdown the proteins found in that organic material. Just like "Scent Killer" and others.
Wow! You sure you don't have a hunk of meat stashed in a pocket somewhere?Will do. Having already tried the soak and water at the car wash when we flew out of the field twice, then the long Dawn soak and wash twice, I sprayed it down with an enzymatic pet urine spray last night and this morning that seemed to make the most difference. Still smells like ass, but at least not one thats been dead and decaying for weeks. I did go ahead this morning and put it in the tub with some clothing detergent and will scrub it again when I get home from work. Just need to get it out drying soon as I need to pack it Sunday for the next sheep trip if I am going to take it. It smelled less enough this morning that I think I could deal with it--but will say the darn slight downwind breeze on the last 7 miles of our pack out was miserable because of the smell--at least made me forget how bad my shoulders and hips hurt.
On that issue, man I wish I could run a Kifaru belt/harness with that bag. Love the way SG frame fits me, and absolutely love the bag, but carrying my brother's and wife's Kifarus a couple times now, sure admit I like their belt/harness design a lot.