Washcloths absorb body oils and soap residue, and these may leave behind funky odors if they are not completely removed during the wash cycle. If the washing machine is overloaded or the cloths aren't placed in the dryer immediately afterward, they may end up smelling less than fresh.
Mix liquid laundry detergent into a bucket of 2 gallons hot tap water to pretreat stained washcloths. Use the same amount of detergent typical for a load of laundry as the extra soapiness helps release stains. Soak stained washcloths in the liquid, swishing around the water a bit as you add the washcloths. Allow them to soak overnight or for several hours. Skip this step if the washcloths are not stained but do not smell fresh.
Place the washcloths in the washing machine along with similar laundry items such as two or three bath towels. Do not add more than three bath towels as the machine needs to agitate.
Select a hot-water wash cycle. Add laundry detergent to the machine as it fills with water, along with 1/2 cup baking soda.
Add 1 cup vinegar to the final rinse cycle.
Remove the laundry from the washing machine after the final spin cycle completes. Inspect and smell the washcloths. If they do not look and smell clean, wash them again, adding 1/4 to 1/2 cup vinegar to the washing machine as it fills with water. Remove the washcloths after a complete wash, rinse and spin.
Place the washcloths in the dryer immediately. Run them through the dryer on the setting you prefer for towels and washcloths, then remove them once they are completely dry.