Take the cushions outside for cleaning, if possible. This is the least messy way to clean vinyl chair cushions. If you can't clean them outside, take them in the bathtub to clean them. If the cushions are affixed to a chair, protect the floor underneath from the mess by laying down plastic sheeting or garbage bags.
Mix together equal parts chlorine bleach and warm water in a bucket if the cushions have mold or mildew on them. Scrub the cushions with a scrub brush and the bleach mixture until the mold is gone, then clean them with warm, soapy water. Rinse and dry the cushions well. If no mold or mildew is present, move on to Step 3.
Fill a bucket with 1 gallon of water as hot as you can stand it. Add 1 cup of mild dishwasher detergent and mix it up well.
Scrub each cushion with a scrub brush and the cleaning mixture. Work in a circular fashion when scrubbing, and rinse out the scrub brush in the bucket of cleaning solution often. Continue this process until the entire cushion has been cleaned.
Rinse the soap from the cushions with water from the garden hose, or rinse it off under the spout or shower head in the bathtub. If you are cleaning the cushions and they are attached to a chair (not removable) fill another bucket with plain water and use a clean rag to rinse them off. Dry the cushions thoroughly with a clean rag.