If you like a salt rim on the glasses, rub the lime around the edge of the glass and then dip the rim of each glass lightly in a plate of kosher salt. Set aside to dry.
Combine the grapefruit juice, lime juice, orange liqueur, and ice in a blender and puree until smooth. Pour into a large pitcher and stir in the tequila. If youre not serving the margaritas in salted glasses, stir 1/4 teaspoon of salt into the pitcher of margaritas. Believe me, it will make a difference!