Liquid sack in chick

[BuckeyeHomestead]

Hey all! so I just hatched the first batch of chicks from my breeders. I noticed this on chick that has a fluid sack not quite by its rump. it's by the hip sinking down along the side behind it's leg. I've grown up raising chickens and have never seen this, neither have my parents. I'm just wondering if anyone else has encountered this and what they did. if it should be drained or what, I'm not sure. the chick is just as lively as the others and runs around all the time, but that sack isn't the smallest and cannot be comfortable. thanks for any feedback!