I reduced the yield significantly from the amounts listed below. You can adjust the proportion of lemon juice to grapefruit to desired taste. From TexasSweet.com. Yes, you could say I have a serious love for grapefruit.
Prepare the SIMPLE SYRUP: Combine the sugar and 2 cups water in a medium saucepan. Stir well and set over medium-high heat. Bring to a boil then reduce to a slow boil and cook, stirring occasionally, until all of the sugar has dissolved, about 5 minutes. Set aside to cool to room temperature or set in an ice bath to chill quickly.
When ready to serve the beverage, combine the lemon juice, grapefruit juice, and the sugar syrup in a medium pitcher. If desired, the mixture can be diluted with a little bit of filtered water, to taste.
Add a grapefruit slice to each serving, fill with ice cubes and garnish with fresh herb of choice.