This how I used to do it....
1.) Spray the car from a very good distance so only the mist of the hose would wet the cars paint.
2.) With the remaining time on the clock I would fill my bucket half way, add soap and fill the rest of the way.
3.) Hand wash the car.
4.) From the same distance as I was when I pre-soaked the car I would rinse it with the gun.
I have never had any problems because I stand so far away from the car. I put my hand about 2 feet from the nozzle and it's only a semi-strong mist of water. It seems like there wouldn't ever be a problem but you can never ever be too safe. It stinks because I need to do this all winter, in the spring, summer and fall it's always washed by hand. I am a clean nut and the car MUST be cleaned every time I use it, I go two days at most without having it cleaned. Considering I have a car cover I really make sure the car is clean.
I don't know what I would do is a huge flake of paint came off my car from the spray gun, I swear I think I would get gray hair, pass out or just ...... I don't know man, I don't even want to think of it.