You shouldn't taste it much after a few gallons, unless some dumkoff poured water into your fresh water tank and ran the pump, even worse if you got some antifreeze in your hot water tank too.
If you can taste it still... some places that can be missed when you de-winterize it... the water fill for direct outside connection. If you are filling your tank and running the pump, drain off the pressure completely, press the check valve on the side of the rig where you connect the hose, then have someone start the pump. Pink?