Cook the macaroni according to package instructions. Cook until the pasta is done. But THEN cook it two more minutes. You want it slightly over-cooked.
Drain the pasta and run under cool water. Set aside to cool. Sometimes I put it in the fridge for a while to cool it down.
In a medium bowl, combine the mayonnaise, milk, vinegar, pickle juice, sugar, salt and pepper. When pasta has cooled down, add the dressing to the macaroni and fold it in gently to combine. Stir in the carrot and the onion. Garnish with a little green onion. Chill at least 4 hours before serving.