Nothing ruins a bowl of clams, mussels, or cockles like a broth full of grit. Keep sand where it belongs—between your toes, on vacation—by cleaning and purging shellfish properly. (Use this method when making the easy Sheet-Pan Clambake.)
Rinse shellfish under running water to remove loose sediment, discarding any with broken shells. (Healthy shellfish will close their shells when firmly tapped.)
Transfer shellfish to a large pot of cold salted water (like their natural environment). Refrigerate, stirring occasionally, for 30 minutes.
Just before cooking, lift the shellfish out of the water by hand, so that the sediment remains at the bottom of the pot. Mussels sometimes have small, fibrous “beards,” which should be pinched off.
Spoon out the delicious juices when serving. Any grit released during cooking will fall to the bottom of the cooking liquid, where it should stay.