[JandC]

When our black gate valve froze last year, prior to pulling out for Florida, the temps only came up to around 30 degrees the next day. Like you I kept the furnace on. I let it run all night and into the morning set on about 75 plus a ceramic heater in the basement. I crawled under the Montana and carefully used a heat gun on the black discharge pipe. After about 45 minutes of that my valve finally released to I could dump the tank.

From that point on whenever any of my tanks get closed in temperatures under 32 degrees I add RV antifreeze to them. Never had an issue since that time and it was 14 degrees when we got up this morning.