Water drain system on 82 FC 35

[davidkerryedwards]

Having just repaired freeze breaks in my plumbing I'd like to get a
conceptual grasp of how the drain system works for the plumbing. I
know there's a manual drain under the vanity and an external faucet in
the propane compartment. I also see three cable operated valves near
the hw heater and tank in the back but I don't understand how they
work. How do the hot water heater and water tank drain and does
anyone have an easy way of retrofitting a system which gets antifreeze
into the system? Since there are no bypass fittings on the water
heater it seems virtually impossible to get antifreeze in the hot
water pipes.

Kerry