My $.02:
Despite how hard I work to try and keep my air lines dry, moisture always seems to accumulate in the air lines. So, here's a tip that I saw on one of the "garage shows" on TNN.
When running an airline, be sure to avoid placing the outlet fitting at the bottom of a pipe. Take a "T" fitting, put a water trap on the bottom of the T, and then run your hose fitting just a little higher up. This will make sure that all of the moisture runs to the water trap, and not to your airline.
A pic would probably help:
