Not sure what plumbers AF is - unless you are talking about and alcohol mixture.
I use a gasous(sp?) mixture a high nitrogen/oxygen content. If it freezes, it means Al Gore was right, and I have bigger problems thatn a cracked block.
I learned that if you mix orange and green, you get jello that doesn't dissolve back out. so I am giving away my stock pile of orange, and will drain off any in my systems that have it.
You really want to use NONTOX RV antifreeze.... it's usually pink.
If you use the NONTOX then you can just hook the muffs up in the spring and let it flow down the drain without the fear of the EPA knocking at your door....