In a large bowl, combine rhubarb and sugar. Toss to coat. Cover and refrigerate up to 5 days, stirring once a day.
Strain juice into a container. Reserve strained rhubarb for another use such as rhubarb bourbon old fashioned. Refrigerate syrup up to 2 weeks or freeze until needed.
Use as a mixer for cocktails like rhubarb bourbon old fashioned, rhubarb martini, rhubarb rosemary gin fizz, and rhubarb shrub.