Into an electric blender, put 2 cups of chopped datil peppers, and 1/2 cup vinegar. Blend for 5 minutes. Put mixture into a saucepan; add 2 large bottles of catsup and 2-1/2 cups of vinegar. Bring to a boil and simmer for 10 minutes. Cool slightly and pour into small bottles.
NOTE: These peppers have a high Scoville Heat rating. Wise cooks will wear gloves and goggles when processing or simply dicing them. When processing 2 cups for sauce, those who are most prudent will wear a mask, as well.