I usually hold the gun rags until I have a load of shop rags to go in as well. Put them in a bucket (in the garage) with detergent and warm water, sit it outside in the sun for a while (while I cut the grass or something else) dump the water in the flower bed (yes, the flowers are okay!) then run the load as a normal heavy load. After the load is done, run it again to get rid of any odor left behind.

Side not on cleaning gun rags, DO NOT use fabric softener in the load. Nasty stuff. Can lead to nasty on the guns, especially rust blued guns. (personal experience)