The nitro is said to attract water, but your hot engine will evaporate the nitro in it pretty darn fast, and all that is left is oil. If you are in a really humid climate, I would consider putting Marvel tool oil in it after use, but if it is dry, I wouldn't waste the time. Running all the fuel out of it runs the oil out as well. I don't know if it is right or not, but I have been told by people that know more about it than myself that the engine will do more damage in that short few seconds of heating up as it quits than leaving the fuel in it. All I know is I have never had an engine go bad not running it out, and friends that run it out and use after run oil religiously change a lot of bearings. One guy that has always run it out and oiled afterwards listened to what I had to say and doesn't run it out any more. I will have to ask the next time I see him when the last time he changed a bearing was. I think i already know the answer though.