In your photo the water heater is in normal operation. The three red arrows point to the valves for the water heater and you need to turn each of them making the top and bottom valve perpendicular to the water line and the middle valve so it is parallel to the water line. The water heater is now in bypass.
The yellow arrow points to the valve for the anti-freeze pickup line. It needs to be turned so the valve is parallel to the line in order to pick up the anti-freeze from the jug.
The black arrow points to the valve for the pickup from the fresh water holding tank. You need to turn this valve so it is perpendicular to the line or you will end up putting anti-freeze in the fresh water tank.
Once you have these valves turned the way I outlined you can turn on your water pump and start drawing anti-freeze into the trailerís water lines.