Important point here to note. If you gas up your keg to 30PSI, you MUST purge your keg before you hook back up your gas line, or else you may have a backflow into your CO2 line & possibly regulator if you don't have a check valve. Probably a no-brainer, but I've done this before. Most of the gas posts on my past kegs were long enough that they break the surface of the beer because I typically would fill my kegs up as much as possible, not really paying attention to where the bottom of the gas post was.
