Use your low point drain, NOT the tank drain. If there is antifreeze catch it in a jug and reuse it each year. If the hot water heater is full you will need 6-10 gallon jugs to catch it all.
Same with the fresh tank. Just open the drain valve and catch the antifreeze if it comes out. Again you may need several gallon jugs depending on how full it is. Not very I will guess.
To winterize put 1 or 2 gallons more than the hot water heater holds in the fresh tank. Pump it through all the pipes hot and cold, to the faucets, toilet, shower, etc. Then drain the hot water tank and cold lines at the low point drains and then drain the fresh tank back into the jugs. Lastly blow out the lines. You can use the same 8-9 gallons for years since the only loss is some for the p-traps that comes out of the faucet and a cup or two that blowing out leaves in the water line.
I have been using the same antifreeze for years and only topped up one gallon last year after 4 years.