Rhubarb, Grapefruit and Thyme Cocktails

((60 ml) Rhubarb-Grapefruit syrup (recipe follows))

((60 ml) vodka)

((60 ml) freshly squeezed grapefruit juice)

ice

rhubarb chopped into ~2-inch pieces

rind of half a grapefruit (, peeled into ~2-inch strips)

sprigs of fresh thyme

granulated sugar

water