Where is the valve to drain freshwater tank

Look around the sides of the fresh water tank, near the bottom of may actually be on the bottom of the tank, depending on your individual model. Ours is near the water pump, but a separate fitting off the tank, it then has a separate valve before leading to the 1" drain pipe to the bottom of the RV. Our old trailer just had a screw cap on the drain pipe.
On ours, the pump and fittings are on the opposite side of the RV from the fresh water fill and vent fittings.

Ken