I'm confused, can you reach those two tank valves easily? They would have to be closed for the bypass to work.
A three-valve bypass would have the two tank valves closed and the bypass pipe valve open. This blocks the anti-freeze from going into the tank, while allowing the antifreeze to go from the cold side to the hot side through the bypass pipe.
For normal operations, both tank valves need to be open, while the bypass valve is closed. The bypass valve needs to be closed so the cold water doesn't bypass the heater and dilute your hot water.
The newer factory installed bypasses only used one tee valve in the cold water line, a pipe to a tee in the hot water line, and a check valve in the hot water line between the tee and the tank. The check valve keeps the anti freeze from back flowing into the tank when bypassed. Only one valve to flip.
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