We were in Flagstaff overnight and had a hard freeze. I was all set for the cold & kept everything operating with no problems. I purposely didn't hook up the sewer hose due to the cold - kept it overnight in the heated storage compartment. In the morning, I hooked up my nice warn not-frozen sewer hose and then "yanked" the black tank dump valve. Turns out the valve was frozen (outside the trailer skin, duh) and I pulled the metal rod right out of the valve.
We spent the rest of the day emptying the black tank into a bucket (manual dump - ugh!), then replacing the black tank dump valve. It's a good idea to "be gentle" with your dump valves in cold weather!
The DW gave me a gold star in lieu of yet another participation trophy - there's no room left on the shelf!