You can make a mixture of ingredients such as ricotta, spinach, egg, garlic, Parmesan cheese, and salt. The easiest way to fill the pasta then is to put the mixture in a piping bag and squeeze the filling into each tube. You can also pipe a seasoned ground beef, sausage or mushroom mixture into the rigatoni and either bake it with a sauce or fry the pasta few pieces at a time, then top it with a pasta sauce and bake. Or better still, have them as appetizers.