Boil the ziti in 4 quarts water with the salt until 2 minutes shy of al dente, then drain without rinsing.
Mix the ricotta, egg, basil, pepper, 1 cup mozzarella and 1/2 cup Parmesan.
Spread 1 cup marinara over the bottom of a greased 6-quart slow cooker.
Layer half of the ziti, half of the ricotta mixture in spoonfuls, 1 1/2 cups marinara and 1/2 cup mozzarella.
Repeat the layers, then finish with the remaining marinara, mozzarella and Parmesan.
Cover and cook on low until the center is bubbling and reaches 165°F, 2 1/2 to 3 hours.
Turn off the cooker, uncover and rest the ziti for 15 minutes before serving.