I was just thinking about this yesterday... how topical.
I have owned my lesco tank sprayer for 5 years and have never used antifreeze of any kind in it for winter storage. I have just been hooking up my air compressor to the hose and blowing the hose, and in turn the pump out thru the drain plug. I make sure the ball valve is OFF to the agitator nozzle in the tank while blowing out. Once all the water is out I OPEN all the valves and leave the drain cap OFF just incase any water is left it won't get trapped by a valve, or in a valve, and split it.
SO FAR I have not had any problems doing it this way, It sits in a non insulated storage unit all winter.
Is it too much of a risk to do it this way? I know the manual says to use antifreeze, but unless I'd use about 5 gallons in the tank I can't get the pump to prime dry and suck it into the lines. I would only use the RV stuff, but still don't know exactly where I'd "dispose" of it come spring.