Like IDGuy said. The three valves should be somewhere right behind your water heater. As he said one valve is Cold Water into the water heater. Another is the Hot Water out of the water heater. The third is a Bypass valve that directly connects the cold water line into the water heater to the hot water line out of the water heater. In the picture of my Vegas setup, the valve at the very top on the Red line is the Hot Water Output. The valve on the Blue valve at the bottom is the Cold Water Inlet valve. The valve on the Red line just above the furnace heater duct is the Bypass Valve. The valve positions are for normal operation.
During Normal Operation (using hot water) -- Cold Inlet open, Hot Output Open, Bypass Closed.
Winterization -- Inlet Closed, Hot Output Closed, Bypass Open.
In the winterization position you are isolating the water heater from the inlet and output lines. In this way when you put antifreeze into the water lines you are not filling up the hot water tank with 6 galoons of antifreeze.
Ed & Bev Felker
Retired USAF Col and retired Nurse
Traveling with Lily & Bella ('Teddy Bear' breed)
2015 Vegas 24.1 (E-350)