Bob, Lynn, Twinkie, Kevin, Don, w7, Gene, thank-you for your help. That plastic thing-a-ma-jig wasn't the easiest to work with. A metal plug would have made it so much easier. Anyway, I got it open and the water poured out like Niagara Falls. Then I lifted the pressure release valve - nothing much happened there - don't know if this is how it's supposed to go.
Then I drained the grey/black water tanks - not much in them - have only been using the toilet for occasional wee-wees since coming home from trip. Opened up all the taps - a few sputters - I figure this is normal, since I haven't hooked up to city water or filled fresh water tank since returning home either.
Gene wrote.....You can run the furnace tonight set at 40˚ F. Tomorrow you can finish winterizing. Don't let the dealer scare you. Do it yourself and save some money. RV Antifreeze (it is pink) is available lots of stores. Ours took 2 gallons—I guess that's about 9 liters. There's also a bypass kit for the water pump which makes it all a lot simpler.
The dealer does scare me...and I do a pretty job of scaring myself too. Still intimidated about wrecking something. I have drained all the tanks, opened taps.
Not sure about that bypass valve you mentioned. Furnace is on; I'm set 'til morning. will study John's link, thanks.
I will still take trailer in on Nov. 21. Needs some warranty work - tail-light has been flickering on and off since purchase for one thing.
Can't thank you all enough for helping me through this. One day I hope I'll know as much as you guys, then I can help someone else.
easily distracted by shiny objects