In a large bowl, whisk together macaroni salad ingredients: mayonnaise, vinegar, sugar, salt, pepper, dried mustard, sweet pickle juice and milk until smooth. Stir in macaroni, celery, red pepper, red onion and olives. Chill for 6 hours. If you like a thinner dressing, simply add 1 Tablespoon at a time, of either milk, water, or even more sweet pickle juice, to the finished salad, toss well to combine. Continue adding your liquid of choice, in 1 Tablespoon increments, until you reach desired consistency. Sprinkle with chopped parsley and serve