Water with a splash of vinegar or a few drops of bleach in a good sized container. Some people advocate a drop or two of a mild dish soap to help the water get to the leaves. I don't use soap. Dunk and agitate well but without bruising. Spread the leaves so the solution gets to the inner leaves. Use a salad spinner to remove the solution. Then repeat with plain water. Spin mostly dry. Bag and use as needed.