I never pour rv antifreeze into the fresh water tank.
First, locate the low point drains and open them to drain water out of the lines.
I use the valves to by pass (isolate) the hot water heater, insert the suction line into the bottle of rv antifreeze, turn on the pump which sucks the rv antifreeze directly from the container into the water lines, then open the faucets starting at the rear one at a time, both hot and cold including the shower, tub and stool until the pink antifreeze comes out. the 'left over' antifreeze is dumped down the drains - tub, sinks, and stool.
From your photos, I didn't see where you have a 'bypass' kit installed with a rv antifreeze suction line.
This video might help:
A you tube search and you will find several video showing hot to do it.
HOpe this helps.