Some cautions... On MY RV the idiots who installed the drain put it a good inch above the bottom of the tank, and that means Gallons of water left. So the antifreeze is highly diluted.
I prefer the dry method, Blow, Blow, Blow Blow Blow Blow the lines out.
basically you open all valves. cycle the ice maker, Drain the supply tank and run the water pump for 1 minute (Give or take a bit, time not critical). close the valve to the ice maker then hook up an air compressor set to around 50 PSI (Via a regulator) to a blow out plug you can get at any RV place or Wal-mart.. blow till no more water comes out or you run out of air.
Wait, (in my case I use the air compressor as a timer, when it cuts off it's time) And blow again, like 10 times or so, (Till no more water comes out when you re-blow)
Close all valves
Add Pink stuff (RV Antifreeze) to drains and toilets.
That's about all there is to it..
The advantage.. When you de-winterize, you have to flush all that pink out of the fresh water lines..... Major job.. Tastes nasty too...
Me.. I don't have to do that.
(Or rather I did not the last few years I wintereized)
Today I winterize by a diifferent method.. but that's not an option for you.