Place 3-4 scoops of rainbow sherbet in freezer safe beverage container.
Slowly pour 1/3 to 1/2 can of soda over sherbet, leaving about 3/4 inch space to top of container.
Place beverage container in freezer and chill for 30-60 minutes.
Pour additional soda over frozen treat if desired. Serve with long handled spoon and straw.