For a medium-sized jar, put one teaspoon of dry mustard in the jar; fill to the rim with water. Leave it that way for 4 to 6 hours and rinse thoroughly with hot water. The jar should be odor-free.
Source: Joan Wilen and Lydia Wilen are health investigators based in New York City who have spent decades collecting "cures from the cupboard." They are authors of Bottom Line's Treasury of Home Remedies & Natural Cures and Bottom Line's Household Magic. They are authors of the free e-letter Household Magic Daily Tips.