10 Get some sort of water trap in your airline. Nothing will screw up a paintjob faster than water entering the gun. If you expect to paint a number of vehicles, then a professional dryer system might be for you. As an added bonus, these dryers will also make all your air tools live longer. If you are just going to spray one vehicle, you can get a disposable inline desiccant dryer like the yellow one shown here for a lot less.