Cook roast covered in water (start with hot water) in crock pot overnight on low 10-12 hours. Pour off water and pull meat into shredded pieces. Saute onion in a little butter. Combine barbecue sauce, onions, sugar and juice of lemon with meat in crock pot and cook on high for 1 1/2 to 2 1/2 hours, or on low for 3 to 6 hours.