Ok now I understand the purpose. I will post you some workable cheap solutions.
You are the best Thankyou
The one tank that I had emptied for the winter only had 4 " of water in the bottom, it froze and broke the bottom.
"We 'Prep.' to live after a downfall, Not just to survive."
Perhaps it would also be dependent on the type of plastic and it's reaction to cold. If it maintained a level of flexability and could expand a little without breaking it would be good. if it was a more rigid type then not so good.
Empty the tank and use as much the water as you can to fill plastic bottles that you can use for your emergency water supply. Store them in your basement if you have one. I would use a clean submersible pump and a clean hose. Remember that the water will have been sitting in your tank for a while you will need to add a few drops of bleach to each bottle prior to use if you ever have to use them. Assuming that you cannot turn the tank over cover it to keep out snow. The submersible pump will leave a couple of cm of water on the bottom of the tank. You will need to remove this water. Depending on the location of your tank you may be able to siphon the water out. If not then a small pump from one of those table top indoor fountains might do the trick. Either way there is going to be a workable solution.
You could also use some Propylene Glycol based RV water line antifreeze. It is non toxic in small quantities and you could dilute and flush your tank in the spring.