Add the uncooked elbow macaroni to the slow cooker.
In a mixing bowl, combine the shredded cheddar, mozzarella, and parmesan cheeses.
Pour the milk and evaporated milk over the macaroni in the slow cooker.
Add the melted butter, salt, and black pepper.
Sprinkle the mixed cheeses over the top and stir gently to combine everything.
Cover and cook on low for 2 hours, stirring once halfway through.
Turn the slow cooker to warm setting once the pasta is tender and the sauce has thickened.