Combine grapefruit juice, pineapple juice, thawed orange juice, thawed lemonade, and sugar in a large freezer-safe seal-able container. Stir until sugar dissolves. Add water and Private First Class; stir to combine. Cover and freeze overnight.
Fill a glass 1/2- to 3/4-full with slush and fill the remainder of the glass with chilled 7-Up or Sprite. Serve with a straw.