The 2 bucket method involves washing the car using two buckets. One bucket contains the warm soapy water (bucket 1), and other other bucket contains clean warm water (bucket 2). You always load the sponge with warm soapy water from bucket 1, pass it over the car, and rinse it in bucket 2. Load fresh soapy water from bucket 1, and repeat. It basically prevents you from rubbing dirt over your car while cleaning it.