winterizing flexable water tank?

[newtocruising]

Does anyone have experience and or recommendations for winterizing a Vetus flexible water tank in a pressurized water system? I was prepared to add the marine/rv antifreeze into my fresh water system, but after looking at the Vetus water tank manual I now have questions. According to Vetus you should never put any anti-freeze in the water system because it is poisonous. They also wants me to disconnect and remove the tank from the boat.

However if I use non poisonous (Propylene Glycol) will I be safe?
Basically is if there is any concerns about any negative effects to the flexible plastic which the tank is made of?

The tank I replaced was the same model from Vetus, but about 23 years old and I believed suffered from dry rot. According to the prior owners never had used it and had not ever put any water into it.

I keep the boat in Marshfield, MA. Never had to deal with these question on my older boats.