The pressure release valve on the State Select Gas Hot water heater (40 or 50 gallon) is allowing water from the hot water tank to drip through the copper overflow pipe drain on the side of the house. There is no leak or drip around the valve or tank itself. The safety notice on the hot water tank says the pressure release valve is supposed to be tested once a year by owner. There are no instructions on how to test the valve. How does one test the pressure release valve?