COMBINE CUCUMBERS, ONION and salt in a colander, place the colander on a plate and place in the refrigerator to drain for 3 hours. Rinse the cucumbers and onions under cold water and gently blot them ("wring them out" in a towel) to eliminate excess water. Place cucumbers and onions in a salad bowl, and add the sour cream, vinegar, sugar and dill. Mix well and serve.