Originally Posted by CrawfordGene
The best way to keep the water sloshing around in the potable water tank is keep it half full. Plenty of slosh space and enough water to retain some warmth. 2air has posted the grey and black tanks are not heated directly like the potable water tank. I think their contents probably lower the freezing point a bit, especially the black tank. You could put some salt into them to lower it more, though I haven't tried it. It true the water doesn't slosh in the pipes, but so far nothing has frozen.
I use the pink stuff...not sure a concentration of salt would be a good idea...
Pink stuff will prevent your valves from freezing up also, which are even more vulnerable than the tanks.
No valve...no dump.
Heat on low is the best way to prevent damage to systems. If you have to shut it off due to tunnells,refueling, car ferries, etc, just turn it back on when you get a chance, everything should be OK for an hour or two.