I do both..
Clean Gray and Black Tank to start.
Bypass and drain the hot water heater... Drain the fresh water tank.....Open the low level drain lines by removing the caps. Attach air hose to city water inlet (adapter needed) keep psi around 40.... Open up the faucets including the shower and toilet until water stops coming out.
You will need to get the antifreeze to water pump kit it does not have one. I also use the antifreeze hand pump for city water inlet. and 2-3 gallons of RV Antifreeze.
RECAP the Fresh water drains.
When using antifreeze I connect to the water pump and turn on pump. Starting at the bathroom I go through all the faucets, shower Toilet and finish with the kitchen sink.
To cover the plumbing from the City water inlet I use the city water inlet hand pump easier with two people one to pump and one to open the kitchen faucet. Since I have already done the bathroom with the pump I stop here.
Add Antifreeze to the P traps.
Open up the lover level drains again a little pink should come out.
When all done you can put the drain plug back in the hot water tank and open the by-pass and put the panel cover back on OR you can make a note to your self by leaving the panel cover off to let you know you will have to do that before un-winterizing in the spring.
The second best think you can to for your trailer in the winter is to get it under cover out of the snow, rain and freezing temps...
For Pump
https://www.amazon.com/Camco-36543-P...antifreeze+kit
Pump for city water side
https://www.amazon.com/Camco-36003-H...119J7G8PPVB71C
Air inlet adapter
https://www.amazon.com/Camco-36143-B...QN16F7MR7XNRKT
I also use Damp Rid and hang them in the garage bathroom and living area.. I like them because the are self contained and can not spill.
DampRid 42 oz. Fresh Scent Hanging Moisture Absorber (3-Pack)-FG83K - The Home Depot