The Korky 2x long-life toilet flush valve seal fits Kohler toilets. Designed to replace the original seals on Kohler Aquapiston, class five, and class six toilets. Replace the original Kohler. The proprietary chlorazone ii rubber formulation lasts 2 times longer than other seals and is backed by a hold-up in the harshest environments. Korky red rubber resists chlorine, bacteria, city water treatment, hard water, and well water.