Can the power washer be stored outside in freezing temperatures?

Yes, if it has been treated with Pump Saver (Part # PW64511-$7.95) or RV antifreeze. The Pump Saver bottle has a molded cap that allows direct connection to the water inlet. Each bottle has 4 to 5 treatments. Otherwise it must be stored inside to prevent freeze damage. There is water in the pump that cannot be completed drained out of the unit. The Pump Saver conditions and protects the valves and seals inside the pump in any climate.