TT winter dry or almost dry camping

Hello All.

When we were shopping for our TT we had a salesperson advise that we could camp in the winter if we created some sort of sludge mixture of water and salt (and perhaps some other ingredients that I don't remember) in the gray and/or black water tank.

In our TT the fresh water tank is under the bed and could be kept from freezing by the furnace that warms the interior anyway. Ditto for the plumbing hoses to the various sinks or the tub.

So, afaik, the only liquid that would be subject to the cold of winter and not heated in any way (short of an electric tank heater) would be the gray and black water tanks.

Is there any way to keep that water from freezing?
I could see just antifreeze in the gray water tank.
Would antifreeze in the black water tank interfere with the chemicals that go in there to break down waste?

Thanks, in advance, and
Happy Camping!