Closing pool: bottom drain

[mirsiniri]

Hello I tried to blow air to clear the bottom drain pipe with a Shopvac 5hp, via the pipe from the pump side. However even though I tried, I didn't see any bubbles coming up from the bottom drain. I was told that an alternative would just be to pour antifreeze into the bottom drain pipe (from the pump side) which I did. Is this true that this would offer sufficient protection for the pipe during the freezing winter? Thanks!