I will shut off the heat to my seasonal cottage water system, draining the sediment filter and water heater along with all the lines. But what do I do about the newly installed water softener re: preventing freezing?

I was told by one plumber to use an external pump to inject RV Anti-Freeze in to the softener and then run it all out in the Spring. I am wondering how effective this would be, and if the poisonous? nature of the RV Anti-Freeze could be neutralized by flushing the system thoroughly in the spring with fresh well water. Another suggested installing a spigot in the lower part of the tank (drilling in to it). Good idea?

Any experience with this? Any other suggestions? Thanks.