Place meat, onion, celery and green pepper in Dutch oven; cover with water. Cover tightly and cook slowly 2 1/2 to 3 hours or until tender. Remove meat; cool, shred and return to cooking liquid. Add catsup, taco sauce, brown sugar, vinegar, garlic, bay leaf, salt, mustard and chili powder. Cook slowly 1 hour. Remove bay leaf; serve on buns.