Good Housekeeping recommends attacking old stains using a mixture of a few drops of a mild dishwashing detergent dissolved in water. It suggests placing the detergent solution in a spray bottle. The instructions are to spray detergent onto a clean cloth and blot the stain until it disappears, then use plain water to rinse away the soap before blotting dry.
Because older stains are set into the fibers, they are sometimes more difficult to remove. If the detergent is not successful in removing the stain, a stronger cleaner, such as a vinegar solution, is required. Once the stain is saturated, clean paper towels placed over it and weighted down with a heavy object cause the stain to transfer from the rug to the paper towels.
Stains from wine, milk, berries and hard candies sometimes respond better to ammonia than vinegar, although ammonia requires proper ventilation.
It is sometimes difficult to pinpoint areas soiled by pets. If the stain is not visible, the remaining urine creates a bad odor in the home. The Humane Society recommends using a black light to find the spots, as urine stains glow in response to the ultraviolet light. An enzymatic cleaner helps eliminate the odors.