Best way to flush head space of carboy?

I want you thoughts on this subject, what is the best way to flush the head space of a carboy with co2? Just putting the gas line inside the carboy and, slowly, releasing co2? I’m fermenting a Red Flanders ale (with White Labs Sour mix) and I’m taking hydrometer readings once in a while so I want to avoid oxidation.

That will do it! Since the CO2 is heavier than air it will settle onto the surface of the beer.

Keep in mind that oxygen will diffuse through the water in the airlock, and even through the bung itself over time, depending on the type of bung. Over a couple of months, you’ll end up with the same concentration of oxygen inside the headspace as in the air around your carboy. Not that this is necessarily a bad thing in a flanders red - it’s actually necessary to develop the acetic character, although too much headspace could give you too much acetic acid. I think this is your bigger risk, as opposed to oxidation.

Best bet is to top up the carboy to minimize headspace if you’re aging long term. If you start getting too much acetic acid, you might want to be ready to rack to a smaller vessel.

Fill the carboy with sanitizer and push it out of the carboy with CO2 and a racking cane that way you don’t have to worry about CO2 mixing with air and you have a carboy full of CO2.