<<Disclaimer: Verify this information before applying it to your situation.>> My friends, I had an experience at my local McDonald's that I would like to share to help you avoid a potential problem. I often get a vanilla milkshake, but on this occasion, my shake tasted like strawberry. Although I was a mile away, I returned and was told I had a vanilla shake, but the pink indicated that there was some strawberry in the line from the previous shake. Apparently, these lines don't always empty completely. At the time I was not aware if strawberry shakes were GF or not, (they are!), but it could just as easily have been chocolate--which isn't GF. Since then, I always ask the servers to clear the lines and I watch to be sure I get the right shakes. I guess I will give up on the drive-thrus... I hope this tip helps ... Aggie in Central NY