Cook pasta in salted water until slightly softer than al dente. Drain, rinse under cold water, and transfer to a large bowl.
Add apple cider vinegar to the warm pasta, toss, and let cool completely.
In a separate bowl, whisk together mayonnaise and milk until smooth.
Add the shredded carrots, chopped celery, and grated onion to the cooled pasta.
Pour the mayo dressing over the pasta mixture and gently fold until everything is evenly coated.
Season with kosher salt and black pepper to taste.
Cover and refrigerate for at least 2 hours before serving, preferably overnight.
