Well, you'd have to completely drain your aircompressor of any moisture in the bottom and fill it when the humidity is really really low, but that would work pretty well. Remember that even on the dryest of days the humidity is 10-20%, and that always gets compounded by aircompressors. As air leaves the compressors, the pressure drop causes the condensation in the tank to become airborne and leave via your air hose. Dry nitrogen (pure nitrogen is by deffinition dry) is a perfect 0% moisture content. Again, for the 1-2mpg, I'm skeptical, but truth is stranger then fiction.