Remove the rind from the watermelon, cube into small pieces, saving a few for garnish and puree the remainder.
Pour the watermelon puree through a fine mesh sieve into a bowl and discard the pulp.
Pour 4 ounces watermelon juice, tequila and lime juice into a shaker and stir. Pour into a Collins or old fashioned glass filled with ice and top with club soda.
Garnish with a piece of watermelon and lime wedge.
Pour remaining watermelon juice into a pitcher and save for later use or to make additional cocktails.