Yours - which according to you leaves rust on the gun. And then there is mine, which as far as I've been able to see, has never left any rust on my guns. If it did, I'd find something else.
You continue to change what I wrote. I do not leave rust on the gun. I do cause flash rust to form, it gets removed. Frankly you are attempting to make an issue out of nothing.
As for Trucks, Air Brakes. They have a compressor and storage tanks. You don't even know what Tanner Gas is, I do.
Tanks are not uphill. In almost all cases they are below the compressor. Does not matter. Best source of incoming air, a warm to hot mechanical room. Lower humidity. We had to dry our Hangar air to -40 to ensure that the pipes did not weep inside when the doors were open (-20 does happen at Anchorage International, not a lot but it does happen). The compressor plant was inside a (usually) warm to hot mechanical room. Cold days with the wind, all those openings and it got cold (cool to me, cold to most). Goggle Anchorage International, note the Hangar in the N. E. area. Also note it has a North orientation as far as aircraft in goes.
So lets talk compressors. Quincy, made in the USA, up to 25 hp recip units. Do you know what kind of valve operation they have? What is the symptoms of valve fouling? What causes it. How about IR? What crank setup is IR famous for?
Or lets talk about oiless type. Oxygen simulation for an MD11 flight simulator. What is the piston setup? Why air? Keeping Oxygen stocked costs a lot and the maint on an Oxy system is high. That is why modern fighters (and bombers) don't carry oxygen (small emergency tank). They make it in flight.
List me ;the types of air dryers. How many CFM does the average air tool use? Why are die grinder the death of small compressors. How big a compressor do you need to keep up with a die grinder.
What is the hp of a home compressor? Why is it controversial?
As for grease in the gun action, it keeps any stray water drops out as well as fouling.