Place the string beans in a kitchen sink filled with cool tap water. Gently swish them around with your hands washing away dirt and debris.
Scoop up the beans a handful at a time and rinse them with running tap water. Place them in a sieve, allowing them to drain for a few minutes. Drain the water from the sink.
Trim each bean by cutting off both ends, called the top and tail, with a sharp knife. You can also snap the ends off with your fingers. Discard the ends.
Snap off the top of the true string bean with your finger and pull the string down and off. Snap off the tail. Discard the ends and the strings.