i wash my mf towels in warm water with liquid detergent (tide) and add 5oz's of vinegar to the final rinse cycle, and dry them on the lowest heat setting in the dryer wih NO fabric softener/dryer sheet...
p.s. if they're are really dirty, i'll pre-soak them in a bucket with some APC and massage out as much of the dirt/grime, and then wash them.
i'm not married so i don't have to sneak or be careful, LOL...
