For sauce, in a large skillet cook garlic in hot oil over medium heat about 30 seconds. Add black pepper and red pepper. Cook and stir for 30 seconds more. Remove from heat.
Drain clams, reserving juice. Set claims aside. Add reserved clam juice and undrained tomatoes to skillet. Stir in parsley, basil, and, if desired, anchovy paste. Bring to boiling; reduce heat. Simmer, uncovered, for 30 to 35 minutes or to desired consistency. Stir in clams; heat through.
Meanwhile, cook mostaccioli about 14 minutes or until tender but still firm. Drain well. Serve sauce over mostaccioli.