Unfortunately, you will never get all the sand out of the clam. The best method we have found is to place them in your sink, take the spray hose to the outside of the shell using cold water. After you have washed the outside as best you can, fill the sink up with enough cold water to completely cover the clams. Depending on how many steamers you have, add a good dose of white vinegar (or red) and occasionally gently swish them around. Let them sit in the sink for about a half hour. This should encourage them to purge any sand. Drain and spray rinse one more time. Then after cooking them, make sure you serve broth to vigorously dunk them up and down in, to wash off any grit that still may remain.