Dave,
How was you system winterized in the past? With pink?
This is what I have done for the past 5 years with zero problems.
Drain the water tank completely with your pump.
Then drain the water heater and close it up.
Pump the air into the dockside fitting, you do not have to bypass the heater, it will blowout thru the heater and all the water lines.
Use up to 50 psi and it will push all the water out of the lines, no problem with that.
There will be no water left after you let the air blow out for a few minutes.
If you have an ice maker, leave the system pumped up with all faucets closed and the ice machine will cycle and all the water will blow out on one or two cycles.
If you have a clothes washing machine, pressurize the system with air, turn on the machine on warm water mode and it will blow out all the water. Dump a gallon of pink into the machine and go to spin cycle to let the pump in the machine send the pink down the line.
Vacuflush heads, when you do the water system step on the pedal, air will blow out. Pour a gallon or two in the bowl and step on pedal again sending pink downstream.
You then have to disconnect both side of your water pump and drain those lines and let the pump drain out. You do not have to connect the lines back up until spring if you are paranoid.
Pour pink to the shower drains until you hear the sump cycle a few times. Pour some pink into the sink drains until pink comes out the thru hull.
Pour pink (I do 5 gallons total) into the holding tank, macerate the pink out to winterize that side of the system.
If you have salt water washdown you can use air to blow that out.
I also blow out my a/c system with air no pink at all, 1" hose on my system.
Done.
Sprinkler companies do the same thing to winterize every one of their customers without problems. It works, 50 psi will blow out all the water.
Go to marineeast and get their hose to garden hose fittings for the a/c hose size and any other hose size you have to blow out.
Go to homedepot or Lowes and get the fittings to take the air compressor end (usually 1/4") and get it up to garden hose male fitting, I put 1/4" ball valve before the garden hose end so I can control the air flow easily.