Remove old carpet stains using mild dish detergent and water. The process requires two spray bottles, plenty of absorbent cloths and white paper towels. Use a heavy pot as a weight.
Mix the cleaning solutions by placing 1/2 teaspoon in one of the spray bottles along with 1 cup of warm water. Fill the second bottle with cold water to rinse the carpet after the stain removal process.
Use the blunt edge of a credit card to scrape any heavy soil from the top of the fabric before wetting the carpet. Vacuum away any particles you remove so you do not wash them deeper into the fibers.
Spray the soap solution onto an absorbent cloth. To prevent overwetting, do not spray directly onto the carpet. Use the damp cloth to blot the stain. Avoid rubbing the stain, which can cause it to spread. Once it is wet, use a dry section of the cloth to absorb the stain and water from the carpet. Continue the process until you eliminate the stain.
Rinse any remaining detergent from the carpet by spraying another clean cloth with water. Blot the area and absorb the water with a dry towel.
Place a stack of paper towels over the area. Set a heavy pot on top of the paper towels and leave them in place overnight. The paper towels wick away any remaining stain and moisture. In the morning, remove the pot and towels and fluff the carpet fibers.