I've winterized my trailers since 1971, except for 16 years in Orange County, CA, and I drain my lines, then blow them out with compressed air, then pump RV antifreeze thru the pump using clear tubing hooked to the supply side of the pump and pushed into the gallon jug. I buy the antifreeze at Walmart since it is cheaper for the same stuff. Yes I use a built in water heater by-pass.
I do put a little RV antifreeze in the FW tank with the drain open, just a little, until I see pink coming out the drain. In late winter when I head to FL I stop the first night below the freeze line and flush everything out, including the FW tank and close the drains.
A little antifreeze in the sink traps and lubricant for the potty, and its good. Don't forget to pump the antifreeze through the toilet flushing system so it is protected, and the shower as well. If I lived in Phoenix I would just keep a low level of heat on a thermostatically controlled electric heater, if possible, and skip winterizing unless heading up to Flagstaff.
2016 GMC Sierra Crew Cab 2500 HD 4x4
6.6L Duramax + Allison, 3.73 axles