I've seen several posts mentioning that dunking your air rifle or pcp underwater is okay if you do it quickly and dry everything properly.
My advice is, just don't.
A coworker dropped off a Hatsan Jet 2 .22 because his gun leaks about once a month. He doesn't ever use it, but when he thinks to do so it's down to to almost empty. He gave the gun to his boss who offered to leak test it and fix it for him..well, needless to say that although he was reassured it wouldn't rust, that as not the case. Also the leak was never fixed, because it's in my hands now. Well, it's at the house, I worked on it this morning, cleaned it up, changed a few seals and removed 98% of the rust. But just see for yourselves.
I'm not sure why the gun was dunked under water for a leak test when there no where for the air to escape aside from the aurtube and valve assembly which is forward of the trigger area. I found the leak to be coming from the bottom flathead screw, and I also found a mangled oring where the valve plate seals up against.
After clahing the seals, cleaning up the guns polishing parts, and lubing it all up, it was holding air. Now to wait and see if it holds up.
The only part remaining with a bit of rust is inside the barrel, I went through 17 patches front and back and there is still some residual, I need to get a nylon brush and scrub it out with the boroclean I have.