Enclosed underbelly but exposed grey line and valve

[Jefster]

I waited too long to winterize, temps got down to about 30°F one night, not a big deal but it wasn't warming up the next day. So I ran the furnace for a couple hours to make sure everything was good and thawed and then tried to dump the tanks that still had a little in then from our last trip home. Black was no problem, the valve handle sticks up into the enclosed underbelly, but the grey was frozen and I notice the last couple feet of the line is completely exposed.

So if camping in cold weather and it gets below freezing, how so you deal with grey tank? I had envisioned using it a bit in November, but I want to use the tanks and just keep it heated while we're using it until we can dump. But if the grey valve is going to freeze regardless, it seems the grey system is unusable.

How do those of you who camp in the cold deal with an exposed grey valve?