Combine grated Cheddar and mozzarella and set aside.
In a small saucepan, heat milk until near boiling. Turn off heat. Melt butter in a heavy pan large enough to hold the pasta after it is cooked. (It will take at least a 14-inch saute pan or a large casserole that can take direct heat.) When foam from butter recedes, remove from heat, add flour, and mix well. Return to medium-low heat, and, stirring occasionally, simmer for 2 to 3 minutes to cook, but not brown, the flour. Gradually stir in hot milk. Raise heat to medium-high and continue stirring until mixture is smooth and thick (about 5 minutes). Add Parmesan and Romano cheeses. Whisk until smooth. Add Tabasco and white pepper and blend.
Cook rigatoni in boiling salted water about 4 minutes. (It will be underdone, but will finish cooking later.) Thoroughly drain rigatoni and fold it into the cheese mixture.
If cooking immediately, preheat oven to 375 degrees.
Layer one-half the rigatoni mixture into a 9x13 pan. Top with one-half of the Cheddar and mozzarella. Repeat layers. Top with chili powder, sprinkled evenly over top.
If not baking immediately, cover tightly with plastic wrap and refrigerate or freeze. When ready to bake, drizzle the 3/4 cup milk over the dish. Bake for approximately one hour. If frozen, add at least 20 minutes to baking time. The dish should be rusty brown on top. Should it appear to be browning too fast, cover with foil for part of cooking time. Be sure to check for doneness in the very center of the dish.