I use a method I learned here on the forum. My gas dip tubes are cut so they are flush with the inside surcace of the keg, or actually recessed a bit. Blow all the sanitizer you can out the liquid side, then pressurize and invert the keg and let the remainder drain to the to the top for a minute. With the gas post positioned to be the very lowest point, pop on a gas QD and blow every last drop of sanitizer out! (Especially helpful if you've trimmed your liquid tubes to avoid picking up sediment.)