I don't know if it has a check valve or not but I drain my heater through the low point drains. I open the outside shower and all inside faucets, both hot and cold sides plus the water heater relief valve and leave them all open, including low point drains, all winter.
After draining the water lines and supply tank, I turn on the pump for 10-15 seconds to pump any residual water out of it. I also put a broom handle in the toilet because the water vlave will hold water and freeze and burst. I also pour a small amount of anti-freeze in the sink and shower drains.
We approach 10 degrees and often reach 15 here and I have not experienced any froozen pipes.
F250 HD 7.3 Diesel :)
31 Ft RLS Designer 5th Wheel :D