Check the projects for a water heater bypass system. It is made of PVC pipeand three ball valves or by one from WM for a few dollars more. After installing the bypass system, drain the water heater and leave the plug out. Switch the valves to the bypass position and run the anti-freeze through the hot water lines. Non will go into the heater. In the spring, run the antifreeze out of the system, reinstall the drain plug and switch the valves back to fill the heater. It's worked great on North Star for several years.