For most RV's the procedure is the same. Close the valves on the inlet and outlet of the water heater and open the valve between them so you don't put anti-freeze into the hot water tank. The heater bypass may be behind a screwed on removable panel, but in will be on the inside side of the water heater. Drain the hot water tank by removing the anode rod, gives you a good opportunity to examine it, make sure you don't have pressure on the system or you will get a bath. If you pull the relief valve it will drain faster. Next find the water pump. You indicate you have a 2015 model so most likely when you find the water pump there will be a short length of water line "T"d on the inlet side of the pump with another valve. Close off the water supply valve and open the valve on the short water line and dip it into your RV anti-freeze supply and operate the pump and turn on every faucet one by one until you see the pink anti-freeze come out, it will not stain. Do the kitchen sink, both faucets, if you have a sprayer open that one also. Do the bathroom sink, shower/tub faucets and don't forget the toilet. Also, pour some anti freeze in each drain to fill the drain trap, don't forget the shower/tub. The best place to get RV anti-freeze at a decent price is Walmart. Plan on getting at least 3-4 gallons of it. Make sure it is RV anti-freeze. If you have to much it won't spoil. Note - the supply to the pump should always be flooded (don't run the pump dry or you may damage it).
Or you could use compressed air and hook up to the city water inlet and blow the water out of the system but you will still need to put anti-freeze in the drains. You still set the water heater by-pass valves for winterizing. There should be a generic description of winterizing in your owners manual.
If you have a water filter you want to make sure it is empty.
Lastly, drain your fresh water tank(s) and the black and grey water tanks.
2014 Palomino Puma 25RS
2011 F-150 Super Crew XLT
Days camped in 2014 - 23
Camped 2015 - 47
Camped 2016 - 51 done - 6 more planned so far