Pour liquid smoke over brisket. Rub with onion salt and garlic salt. Roll brisket in foil and refrigerate overnight.

Preheat oven to 300 degrees F (150 degrees C). Place brisket in a large roasting pan. Cover and bake for 5 to 6 hours. Remove from oven, cool, and then slice. Put slices back into pan.

In a medium saucepan, combine brown sugar, ketchup, butter, water, celery salt, liquid smoke, Worcestershire sauce, mustard, salt and pepper. Stir, and cook until boiling.

Pour sauce over meat slices in pan. Cover and bake for 1 more hour.