I always wonder when flushing with co2 is mentioned how much o2 you really get out of the bottle.
When I flush a keg it is full of sanitizer when I start out but with a bottle, unless you want to do the same thing, it is full of o2
If you could visualize the gases in that bottle color coded, Red for o2 and blue for co2, when you 'flushed' what you would see is the colors mixing to a nice purple. I imagine at some point, if you kept pumping in the co2 it would turn blueish but never blue as the gases would continue to swirl about and mix. I am sure you get alot of o2 out but you will never get it all. so youreduce the contact with o2 but you do not eliminate it. This would be true with a beer gun as well as a picnic tap, number 2 stopper setup so I guess it's not very helpful. I feel like without o2 absorbing caps or bottle refermentation you will never get rid of all the o2 in there.