Cook the pasta in a large pot of boiling, salted water for 10 to 12 minutes (or according to package directions).Rinse with cold water, drain and set aside.In a very large bowl, combine the crab meat, mayonnaise, buttermilk, onions*, garlic, lemon juice, and seasonings.Whisk together until well combined.Add the pasta and toss until well coated. It can be eaten immediately but it's really better if you cover and chill it for a few hours or overnight.