Barbecued Pork Sandwiches

• 20 hamburger buns
• 2 pork loin roasts (boneless)
• 475 ml ketchup
• 240 ml water
• 200 gr celery dice
• 80 ml steak sauce
• 60 ml vinegar
• 55 gr brown sugar pack
• 10 ml lemon juice
• 6 gr salt