Yes, the syrup tax applies on sales of carbonated beverage syrup when sold to consumers for use in making beverages for their own consumption.
RCW 82.64.020 states:
1) A tax is imposed on each sale at wholesale of syrup in this state. The rate of the tax shall be equal to one dollar per gallon. Fractional amounts shall be taxed proportionally.
2) A tax is imposed on each sale at retail of syrup in this state. The rate of the tax shall be equal to the rate imposed under subsection (1) of this section. (Emphasis added.)
Therefore, it is clear that the law intended for the syrup tax to apply on retail sales of syrup to consumers.