Blue line-valve cold in
Red line-valve hot out
Blue/Red line-valve bypass for winterization or as a tempering valve for hot water temp control
Winterize by turning both Red line valve and the Blue line valve closed
Open the Blue/Red line valve (allows water/antifreeze to bypass tank) Don't put antifreeze in HW tank!
Drain tank and plumbing from under RV (Be sure to close the line drains before next step)
Find the loose open-ended hose with valve attached (located in and the HW tank compartment) and place it in RV antifreeze bottle. Open valve, turn water pump on which will draw antifreeze into plumbing. Once you have enough antifreeze be sure to open faucets and toilet tank flush to get antifreeze into these areas.
The link the D provided is the detailed procedure.