A mildew smell can remain on wet clothes even if there are no visible signs of mildew on the clothes. Once you notice the mildew smell on your wet clothing items, just washing them in your washing machine will likely not remove all of the foul odour. This odour can make you consider throwing the clothes into the trash. Pre-soaking the clothes in the right solution before you wash them is the key to removing the mildew smell.
Fill the sink or tub (depending on the amount of clothes) with a solution of cool water and white vinegar. Add 2 tbsp of white vinegar for every 1 cup of tap water.
Soak the wet clothes in the solution for 30 minutes.
Remove the clothes from the solution, and place them into the washing machine. Wring the clothes out to remove excess moisture if you wish, then immediately place them into the washing machine.
Run one entire “cold” washing machine cycle without any detergent or fabric softener.
Run another “cold” cycle, this time with your standard washing powder and fabric softener (if you use it) added into the machine. The amount of detergent and fabric softener placed into the machine varies depending on the amount of clothes you're washing.
Dry the clothes as normal. Inspect for a mildew smell, and repeat the process if needed.