Hello. On a 1 valve water heater bypass the valve has 3 sides or lines
1 Blue line - water supply cold
2 Blue line - bypass from supply to hot line "tee"
3 Short line to water heater inlet
So how does this work?
In normal mode water goes thru valve with handle in line with supply and water inlet to heater and out the heater outlet it does not go up the bypass line. When you turn handle on valve to the "Bypass" position the water comes in to the valve then exits out the bypass line to a "tee" in the hot outlet line it can not go back in to the water heater because there is a "check valve" at the water heater that only allows flow out of the heater. This allows anti freeze to flow into the hot water lines.
If you are using anti freeze to winterize you
1 open drain on water heater located outside and drain water heater leave this drain open
2 At your pump there should be a valve to add antifreeze. Turn that to the suction line that you put in the anti freeze jug and turn on pump
3 Run pump till anti freeze comes out of the water heater drain then turn your Bypass valve to the Bypass position -up and down-and do all the faucets and don't forget the outside shower and toilet.
This is mostly instructions on bypassing the water heater if you need more detailed instructions on winterizing just ask and you will get lots of help.