I am assume you are referring to what is called an “ice dam” some where in the drain pipe
Building codes don’t require a “steeply pitched” drain pipe. So, if debris especially stuff from a wash stall, hair, muck, straw, soap etc doesn’t get completely carried out of the drain it will cause some back up and slow the “water stream” and cause an “eddy” effect. Even though the majority of water will flow over it in very cold conditions it freezes. Continued use causes the “dam” to build up layers of ice until you get a “freeze plug”, ice dam. IMO when a wash stall drain is being installed the drain pipe should be run at as steep an angle as possible.
That being said mixing up a bucket of hot water with as much calcium chloride (road salt for low temps) that will dissolve should do the trick. Something that I have never tried but may work quite quickly is drain cleaner. The stuff you use for clogged sinks and such. The chemical reaction in this stuff heats up which is why it works on grease and such.
If this is a persistent problem it maybe worth snaking a heat tape into the pipe when it clear and leave it there. Only turn it on when there is a problem. Have not done this myself but I know of others that have.
Another thing to do with problematic drain pipes is to be proactive by cleaning the drain periodically with one of these;
http://www.homedepot.com/p/BrassCraft-Large-Drain-Bladder-BC00333/100569152
Get one that fit’s the ID of the drain pipe and attach a hose to it. Push it through the pipe until you encounter the clog or as far as you can go. These have a small “outlet” that is tightly closed. When the water is turned on it will expand like a balloon inside the pipe and hold fast. When the pressure builds up enough the water will “burst” through with a lot of force and “jet” clean the pipe of debris build up.
The above may or may not be of help it’s based on a limited description of the problem.
I don’t think anti-freeze added after the fact will be of much help. Anti-freeze doesn’t freeze in its self but I don’t believe it “melts” ice it comes in contact with. We’ve got plenty of ice around right now so I might have to entertain myself by seeing what happens when anti-freeze is added to a container of ice.
