Preheat frying pan at 350 degrees; melt butter. Add pork and saute about 2 to 3 minutes or until meat is browned. Drain pineapple, reserving about 3/4 cup of syrup. Combine pineapple syrup, Russian dressing, water, cornstarch, soy sauce, vinegar, and salt; pour over meat and stir until thickened. Cover. Turn heat down to a low simmer. and simmer 30 minutes or until meat is fork tender. Add green pepper, onion and pineapple tidbits. Cover and cook 5 minutes. Serve over hot rice.