The Blichmann gun has 2 triggers on it, one for CO2 and one for the beer. To purge, you put the gun all the way into the bottle and give it a good 5 sec. blast of just CO2. That pushes out the O2 and helps prevent the beer from picking up any oxygen that can lead to off flavors from oxidation. Immediately after you purge, then you press the trigger for the beer and also fill from the bottom up. Another tip, don't squeeze the beer trigger halfway or slowly, give it a good quick pull so that the valve opens all the way quickly. If you only squeeze half way or slowly, it will throttle the beer through the valve and cause it to foam up on you. It can be a little frustrating the first time you use it and it may take you a few times to find the set up that works best for you. But I've stored bottles for a few months and they've all turned out fine. Good luck!
Draft 1: Belgian Chocolate Stout
Draft 2: Belgian Wit
Draft 3: Double IPA
Primary 1: Irish Red Ale
Primary 2: Weizen
On Deck: Imperial Stout, Berry Wheat