[Greg Stoddard]

There is always moisture is compressed air, it's a by product of heating the air as it is compressed and it then cooling in the tank. There shouldn't be enough to cause any issues with the amount that gets in the tires. There are driers and water traps that can be added to the outlet line from the tank but they require upkeep and that wouldn't really happen at a gas station so they don't bothr with them.

 

[William Wiles]

Press the valve and let the air blow out of the hose for a minute or two. It will purge the condensed moisture in the hose.