How long are you going to ferment for? If it's just a couple weeks, I'd bet youd be fine. I use 5 gallon buckets with lids and don't seal them really tight - just gravity. The yeast make CO2 and that kind of pushes the oxygenout/yeast probably eats a bit too.
So far I've had good luck. You have to watch for the CO2 production to stop/kreusen to fall. You might get some oxygen after that point. I try to minimize that. (I'm assuming you're brewing on a limited budget like me.)
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