If you already notice mildew forming on your curtains, check the cleaning label on the fabric to see if it’s machine washable, and if it is, toss your curtain in for a quick wash cycle while the vinyl liner air dries. If you wash the curtain by hand, soak it for 15 minutes in a solution with equal parts vinegar and borax with added water, then grab a sponge and scrub away the mildew.