Moisten a bath towel.
Lay it flat.
Dump the .22s on the towel.
Fold towel over .22s and let sit for a couple minutes, to moisten the mud/clay residue.
Rub around to clean the rounds.
Dump elsewhere, and allow to dry.
Lather, rinse, repeat, until all .22s are "clean enough".
I would rather not toss them in the trash and have one go off when the truck crushes them.
Should I toss them in the bottom of a pond?
Either one would be illegal disposal of hazardous waste. Don't go there.