Winterizing question ??????

[polarlyse]

We have an '85 Excella 31 footer. I've been reading about winterizing AS's and see some mention of water heater by-pass valves.
Were they standard on these units or after market installations ?? My water heater is on the curb side below the bathroom vanity. I don't think there is any easy interior access. From the exterior access door I have access to the supply line and a drain valve. How would I know if there was a by-pass installed ???

I plan to blow the lines and install RV anti-freeze to the traps. If I drain the water heater tank, blow the lines and leave the drain valve open is that adaquate for winterization of the water heater ??? I also plan to disconnect the lines to the pump and leave them off . Any further advise is welcome. I plan to use it in the coming weeks and will winterize upon returning home.

Thanks in advance for all you're input.
R. Kriz
New Jersey