I not sure what the big boys (BMC) do but small craft breweries often use a multi head counter pressure filler (does 2 or 4 or 6 at once) by
hand. there a lots of brewer blogs where start ups discuss the woes of bottling. One thing I have learned researching my own real micro brewery is bottling no matter how you do it unless you have a $100,000 fully automated bottling line SUCKS BALLS!!! My understanding of those bottling lines is they are just counter pressure fillers with conveyor belts and sensors. CO2 pressure followed by beer, no real purging. Why would they bother, CO2 displaces O2 and pushes it up so any CO2 in the bottle will be on the bottom where the beer is going in and remain as a blanket on top of the beer as it fills, pushing the O2 out at the same time.
When breweries bottle their beer in Canada they put a best before date (I don't know if they do that in the states) that date is typically 6 months after the bottling date (some put both). They are not intending it to last years, or even a year they are intending you drink it ASAP. They are also intending that the beer be stored in cold conditions as much as possible (even though that only happens in private liquor stores that care about product quality, that's a completely different issue).
Even so there are people on that sticky that have stored beer bottled with this tool for over a year with no issue, and I don't believe there is any oxygen left in the bottles that I fill this way. There is beer and foam over flowing over the top when capped. Where is all this oxygen coming from? (where as beer that is bottle conditioned has a head space with oxygen in it left on purpose!)
Also most stuff that is meant to cellar for long periods even today is bottle conditioned, not force carbed. I don't think many breweries that bottle condition are bothering to purge with CO2 before filling but I could be wrong about that. Even if you did it would be hard to ensure that the oxygen stays out unless you are pushing flat beer using a CO2 system similar to a bottling gun.
If you really want to do this post 5
https://www.homebrewtalk.com/f35/we-no-need-no-stinking-beer-gun-24678/#post241821 shows a diagram of an added tire valve with a bicycle pump attachment hooked up to CO2. I think this is a waste of time and CO2. CO2 here is $35 for 5 pounds so I treat it as more valuable then the beer its self!