1 (20 oz.) bottle Gatorade (or larger)
1 quart 100% Grapefruit juice
2 tbsp. sugar, honey or agave syrup, or to taste

We like to use pink or red grapefruit for this.

Drink the Gatorade (we only want the bottle).

After the bottle is empty, fill it with grapefruit juice and add the sweetener. Shake well to mix.

Freeze. Shake the mixture every hour to break up the ice crystals. Continue to shake every hour until slush has formed.

Variation I: Party drink - add an ounce of vodka or gin to the slush mixture before freezing. It will keep the larger ice crystals from forming and the slush will be smoother. If slush has too many ice crystals, process briefly in a blender.

Variation II: Cold drink-to-go - fill bottle 1/2 way with grapefruit juice (or other fruit juice). Freeze until solid. Before leaving the house to go on your trip, fill the remaining space in the bottle with more grapefruit juice. The bottom half will act as an ice cube but will not weaken the drink while it thaws.