A good easy way to get the clams to spit out sand is to take the clams and place them in a bowl or container large enough to fit the clams in.
Then add some cool tap water to the bowl or container with the clams in it.
And the clams should be starting to spit out sand and you can also cause the clams to spit out even more sand by adding some cornmeal or black pepper to the water that the clams are in.
The clams will then start spitting out even more sand and should get rid of all the sand inside them so they'll be ready to prepare and eat.
It can take from 20 minutes to a full hour for the clams to spit out all the sand so I would allow the clams to stay in the bowl of water for an hour to allow the clams to spit out the sand before you're ready to eat them.