Italian Cooking Primer
Selecting good clams is essential to executing this dish. Use the smallest, freshest clams available. Pick clams with closed, unbroken shells, which usually mean that the clam inside is alive. To test, tap the shell a few times on the counter. If the shell closes, the clam is alive. If it stays open, it is not and should be discarded. Try to avoid buying clams sold in tightly packed bags that make it seem as if the shells are closed.
To clean fresh clams, scrub with a kitchen brush and soak them in cold water. Scrub again and soak again. Drain the water and continue soaking until the sand and grit are removed and the water is clear.
Greco di Tufo
National Pasta Association Recipe