Add rhubarb and water to large pot and boil until soft, approximately 15 minutes.16 cups chopped rhubarb8 cups water Using food mill or strainer, strain liquid into large bowl.
Add pineapple juice, sugar, and lemon juice. Mix. 4 cups pineapple juice3 cups sugar1 tbsp lemon juice Freeze in ice cream pail or large freezer safe container overnight.
To make slush, put a scoop of this in a glass and add lemon lime soda or sparkling water to taste.