Carpet underlay makes carpet more comfortable to walk on while protecting it from premature wear. However, this useful bit of padding can also make cleaning carpet stains tougher. Heavy liquid spills soak through the carpet and into the underlay where they may go unnoticed until they begin to smell. To clean liquid stains that have penetrated the underlay, use an odour-fighting detergent before an odour develops.
Place towels over the spill to soak up excess liquid. Place something large and heavy (the heavier the better) on the towels to put pressure on the stain. Replace the towels around every 15 minutes. Stop when no more liquid is absorbed by the towel.
Neutralise the substance embedded in the carpet padding with a commercial cleaner. Use an enzyme-based pet stain cleaner for urine and other organic stains. Dilute an oxygen bleach cleaner with water according to the manufacturer's instructions for other types of fresh stains, or use a 50/50 white vinegar and water solution. Apply the cleaner to the stain following the manufacturer's instructions. Use enough to saturate the carpet and the padding underneath. Allow the product to sit for the manufacturer recommended amount of time (5 to 10 minutes is enough for the vinegar solution).
Blot up the cleaner using the towel compression method described in step one.
Saturate the stained area with water to rinse out any cleaner residue.
Blot up the water using the towel compression method described in step one.
Monitor the stained area over the next week or so. If there is an odour, flush the area with water using a wet/dry vac according to the manufacturer's instructions. Load the machine with clean water (no detergent), then use it to force clean water through the carpet and padding underneath. Vacuum the excess water up. If the smell returns after this treatment, you may need to replace that section of your carpet's padding.
Do not use white vinegar on pet urine stains. You may not be able to smell the stain, but your pet will and he or she will likely revisit the spot. Test any cleaning solution on a small, inconspicuous section of the carpet before treating the stain.