1. In a bowl mix sugar, vinegar, oil, salt, pepper and celery seed. Set aside.
2. Drain cans of beans.
3. Place beans into large container (with cover).
4. Chop onion and mix with beans.
5. Pour mixture over beans.
6. Allow beans to marinate for about 24 hours before serving. (Stir occasionally.) Keep refrigerated.
7. Drain liquid from beans before serving.