To make the syrup, combine the rhubarb, strawberries, sugar, orange peel, and water in a sauce pan. Bring to a boil over medium high heat, then reduce heat to a simmer, and continue to simmer for about 10 minutes, stirring occasionally. Use a potato masher to break up the fruit until it's fairly smooth. Cool and store in the fridge until ready to use.
To assemble the floats, fill glasses with a few scoops of vanilla ice cream. Combine the club soda and syrup together then pour over the ice cream. Top off with a little extra soda, if desired. Alternately, if you'd like to just mix up one or two at a time, combine about 3/4 cup of soda with syrup to taste, pour over ice cream, and serve.