How to actually clean your ruck, or how to clean it for an inspection? If you‘re cleaning it for an inspection, usually you just want to clean the visible dirt, so a cloth, and a bit of water usually does the trick for me.
If you want to actually clean it? I fill the laundry sink with warm water, throw in a half cup of detergent, and toss the ruck in (Take it apart first) and leave it to soak for a couple of hours. I usually toss my webbing components in at the same time. After it‘s soaked for a good couple of hours, I take everything out, drop it in a bucket so the water doesn‘t run everywhere, then then vigorously work the items one at a time in the tub (a couple at a time for the smaller stuff).
Then I rinse, and repeat... keep doing this until your rinse water stops turning brown... it‘ll take a half dozen rinses to get the stuff truly clean.
Seems a bit excessive, but if nothing else, do this with the back-pad from your ruck and the yoke from your webbing... there‘s no garuntee that they were well cleaned when they were turned in, and if that‘s the case, they probably have years of built up sweat on them.