Yeah....I think the flavoring people and the plastic tank people are in cahoots! LOL
Actually in the essential oils it is the citric acid that degrades many polymers.
In many flavors it is the Triacetin..." It is the triester of glycerol and acetic acid"...
Note that word "acid"...and it does the trick on plastic!
Here is a simple way to tell if a e-liquid will degrade plastic:
Use litmus test strips and check the pH of the liquid (available at any drug store).
If the pH is less than 7 the liquid is considered to be on the "acidic" side and the lower it is the more reactive it will be with many plastics...
Now there are some "plastics" (not really plastic but look and feel like plastic) that are resistant to low pH, but none are 100% resistant!
Some are just better than others such as Polycarbonate, but it too will eventually degrade.
Also in any set ups you may have that use "O" rings such as for atty tanks, replace the original seals / "O" rings with Nitrile "O" rings as these are much more resistant to the low pH liquids than the Neoprene "O" rings that come with about all tanks...
If any would like, I can post a on-line supplier of "O" rings that is VERY reasonable and has both Std., and Metric in various "resistant" materials...