Preheat oven to 350° F. Place crackers in a large zip-lock type pastic bag and crush with a rolling pin. Finely chop onion.
In large bowl, combine crushed crackers, onion, ground beef, egg, milk and black pepper. Mix well.
Coat a loaf pan lightly with nonstick cooking spray. Place mixture into loaf pan. Bake for 40 minutes.
To make topping sauce, mix catsup, brown sugar, vinegar and water in a small bowl. Remove cooked meatloaf from oven and cover with sauce.
Return pan to oven and bake for 10 additional minutes or until internal temperature reaches 160° F. Slice into 6 portions and serve.