Place meat in slow-cooking pot; cover with sliced onion. Combine garlic, catsup, Worcestershire sauce, sugar, salt, paprika, and mustard. Stir in water. Pour over meat. Cover and cook on low for 9 to 10 hours. Turn control to high. Dissolve flour in small amount of cold water; stir into meat mixture. Cook on high 10 to 15 minutes or until slightly thickened.