We don't get more than a couple of hard freezes a year in Tucson but we will get one tomorrow or the next day. I have emptied fresh, grey and black tanks, relieved any water pressure in the system and will leave the kitchen faucet cracked (with no water hooked up) for room for expansion. We will be in the high 20's and low 30's for 3-4 hours during the night.

Do I a) need to drain the low points and hot water tank or b) need to run the furnace at ~50* overnight or c) both?