Trim fat from brisket. Place the meat in a 3-quart rectangular baking dish.
In a small mixing bowl, combine the liquid smoke, celery seed, pepper, Worcestershire sauce, garlic salt, and onion salt. Rub the seasoning mixture on the meat, coating all sides evenly. Cover and marinate brisket in the refrigerator overnight.
Cover with foil and bake brisket in a 325 degree F oven for 4 hours or until its very tender. Add 1/2 cup warm water to baking dish after 30 minutes of baking.
Pour barbecue sauce over meat. Bake brisket, uncovered, 30 minutes, adding water if needed. Slice or shred; serve on buns, if you like.