Unzip the fabric upholstery cover to remove the foam couch cushion.
Fill a bathtub or large tub with warm water. Add a mild liquid detergent, such as dish soap or delicate laundry detergent, to the running water. Immerse each cushion in the water, and allow it to soak for five minutes
Use a soft-bristled brush to gently scrub away any visible dirt, and clean all soiled areas.
Drain the tub to remove the original water. Rinse each cushion with clean water to remove all soap and debris.
Gently squeeze the cushion to remove the majority of the water absorbed by the foam. Do not wring to twist the cushion, since doing so can tear the foam or damage the shape of the foam.
Take the cushions outside to air-dry thoroughly in the sun. Once one side is dry, turn the cushion over to allow the foam to dry completely.