What can I use to remove the awful smell out of dishrag?

If the dishrag is damp/wet on and off over a couple of days before you wash it, then odor causing bacteria is building up on the rag. If you only wash it with detergent, that's not enough to sanitize the rags and the smell (a mildewy, foul smell) will linger or reappear as soon as the "clean" rag gets wet. Washing in hot water using detergent and 3/4 cup Clorox^® Regular-Bleach (or 1/2 cup New Concentrated Clorox^® Regular-Bleach), will sanitize the rag and eliminate the odor. Be sure to wash with bleach every time you wash the rag!