That is correct, you are suppose to store them with the juice in them. You can wipe it down and then what I do if I am going to be stoing it is stick a straight pin in the nozzle to keep deposits from forming and clogging the nozzle. You need really have to clean them out unless they really really need it.
My first fogger clogged up in the heater unit. Finally tossed it. Now I went through heck with the Chauvet 1250 for the same reason. So I have done the following. I now can run the pump without the heater. So what I am doing is run water through the fogger under a standard fog cycle until nothing but hot air / steam comes out. Then I am allowing the unit to cool down. Once the unit is cooled down I attach my bypass cord to run the pump when it is cold. Instead of fog juice which is expensive, I am pumping good old anti freeze until it squirts out the nozzle. Now I have the pump and heater filled with a non corrosive non oxidizing solution. When I bring the fogger out for next year, I will first pump water through the unit until the anti-freeze is evacuated and the run the fogger on water and then on fog juice.
I know this seems a bit extreme, but I refuse to buy another fogger or go through the tedious process of clearing the clog in the heater.
Leaving fog juice in the pump is likely a good idea, but some of that juice remains in the heater and if it crytalises in there, your toast.