That slight, new plastic smell is what you want to smell. The guy's are right- the syrup won't take that on. I've got some jugs that I've used for years and they still have that "plasticky" smell to them. That's the sign, or smell, of a properly washed out container. Just be sure you rinse/flush your jugs out a few times with only hot water every time you empty them. If you don't rinse well, they will have a fermentation smell to them in short order, which never goes away. They are junk at that point.

Steve