Drain clams, reserving liquid; set clams aside.
Cook salt pork in a Dutch oven over medium heat 5 minutes or until crisp. Remove salt pork, reserving 2 tablespoons drippings in pan. Set salt pork aside. Add onion, and saute 5 minutes or until tender. Add clam liquid, potatoes, and 6 cups water; bring to a boil over medium-high heat. Reduce heat, and simmer, uncovered, 12 to 15 minutes or until potatoes are almost tender. Add tomatoes and clams; simmer, stirring occasionally, 20 minutes. Stir in salt and pepper.
Heat milk and butter until almost boiling; stir mixture into chowder. Stir in basil. Spoon 1 tablespoon whipping cream into each bowl; ladle chowder over whipping cream. Sprinkle with reserved salt pork. Serve with crackers.