Tangy Barbecue Sandwiches

3 cups celery -- chopped

1 cup onion -- chopped

1 cup ketchup

1 cup barbecue sauce

1 cup water

2 tablespoons vinegar

2 tablespoons Worcestershire sauce

2 tablespoons brown sugar

1 teaspoon chili powder

1 teaspoon salt

1/2 teaspoon pepper

1/2 teaspoon garlic powder

1 boneless chuck roast (3 to 4 pounds) -- trimmed

14 14-18 hamburger buns -- split

In a slow cooker, combine the first 12 ingredients; mix well. Add roast. Cover and cook on high for 6-7 hours or until tender. Remove roast; cool. Shred meat and return to sauce; heat through. Use a slotted spoon to serve