In 4 tall glasses with ice add 1/2 tsp. of grenadine. In a cocktail shaker add 1 cup of tequila, 1 cup of grapefruit juice, 1/4 cup fresh lime juice, 2 tsp. of fine sugar and a pinch of salt. Shake well and pour into glasses. Top off each drink with a 1/4 cup of grapefruit soda.
