Place rabbit pieces in a crock, cover with water and vinegar. Add sugar and onion. Season with salt, pepper and pickling spices. Cover, let stand in refrigerator 3 days. Remove rabbit from liquid, dry and reserve liquid. Coat rabbit pieces in flour, and brown in heated frying pan or skillet. Gradually add 1 C. of the reserved liquid, cover and simmer 1 hour or until tender. Remove meat to platter and thicken liquid for gravy.