Try this. Buy 2-3 way valves and hook them to the in and out of the hot water heater. Run a bypass hose between the valves.
In the fall, just turn the valves to bypass the water heater. Open the drain on the water heater and leave it dry.
Been doing it that way for years.
Gary

Sometimes I just hook the cold in hose straight to the hot out so bypass tank, then just drain tank.

You should not run anti freeze through heater drain and by pass. I drain water tank and pump anti freeze through lines without adding to tank. Easier to flush pink out in spring.
Jim

I agree with jim drain your water tank pull the hose off the tank that feeds the pump and put that hose in a gallon of antifreeze run the system as normal till you see solid pink. if you have a hot water heater you must bypass it. A little water left in the bottom of the tank is fine it has plenty of room to expand.

Most of my friends and I just blow the system out with compressed air. I built a fitting to connect my compressor hose to my water intake. The process I use is this: run all of the water out of the tank, leave a faucet open, start the compressor, let air run until the faucet stopps spitting, open the next faucet, close the first faucet (do not leave the compressor running with all faucets closed - system can't handle the pressure), and so on. If your head works off of fresh water make sure to cycle the head a few times while under air pressure too. I usually take a 30 minute break to allow any remaining water vapor to settle and then repear the same. I've never had any problems (I am on Lake Erie - gets plenty cold enough to freeze!). This lets me just sanitize my water system in the spring (cup of bleach, fill and run water out 2-3 times) and off I go.

Hope this helps.