New answers tagged co2
Any way you take a sample (unless it's from a pressurized vessel with an outlet) will draw air in. As you suspect, it should be a small amount, and given that your beer A) may still be fermenting (which CO2 will help strip any introduced oxygen out of the beer) and B) definitely still has yeast in it (which will scavenge oxygen, as long as it's still alive), ...
Since CO2 is heavier than oxygen, it won't escape the container unless you have a wind blowing over the opening. Also, the beer will be generating more CO2 as i ferments, so even if any escapes, more will replace it. I don't think it would be a problem to leave a small hole.
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