Whisk the mayonnaise, sour cream mustard, brine, sugar, hot sauce, remaining 1 Tbsp milk, and 1/2 tsp salt in a large bowl. Add the macaroni, red onion, bell peppers, celery, celery leaves, and parsley; toss to coat. Cover and refrigerate at least 2 hours. Stir again before serving; season with salt. Enjoy!