Rinse the leeks under water to remove visible dirt or sand. Cut off the roots and the dark green tops of the leeks and slice the leeks in half lengthwise. 2. Chop the leek halves into semi-circles. Rinse the sliced leeks in a bowl of cold water. Use your hands to agitate the leeks and dislodge any dirt or sand that may be clinging to them. 3. Pour the leeks into a colander to drain.