Add cucumber and basil to a cocktail shaker; muddle gently with a cocktail muddler, pestle, or the back of a spoon. Add lime and grapefruit wedges and sugar, muddling them gently as well to release juices.
Add lime and grapefruit juices to shaker. Fill to top with crushed ice, cover, and shake vigorously for 20-30 seconds.
Double strain into a highball glass filled with crushed ice. Top with rum and soda, and garnish as desired with ingredients (You can also add the contents of the cocktail shaker if you'd rather not cut up more fruit - it works just as well!)
Pop in a straw, kick back, and enjoy!
Amount Per Serving
Calories310kcalCalories from fat 3
% Daily Value
Percent Daily Values are based on a 2,000 calorie diet. Your daily values may be higher or lower depending on your calorie needs: