Clams ingest some quantites of sand in their environment and need to be purged before cooking and eating.
Place them in a container of clean seawater or salt solution (1/3 cup salt to 1 gallon water) with about a cup of cornmeal. Freshwater should not be used.
Let them soak in the bath for several hours, and they will expel the sand and siphon the cornmeal.
Discard any clams whose open shells will not close when touched. Also discard any of the siphon clams that do not constrict their necks when touched. This is an indication that the clams are dead and no longer edible.