This is my first time brewing and I only started yesterday, so I'm still very much a novice.
I have a bubbler airlock on my 33 litre fermenting bucket, like the one in this image:
I filled it up to about 50% at each side and left the bucket overnight, when I checked it around 7 hours later, it had become empty on one side (right side if that matters). I filled it back up to 50% each side and went off to work, when I checked it just now (10 hours later), it's the same as it was this morning, 50% full on the left side and empty on the right side. I'm currently brewing 20 litres (40 pints) of cider and the temperate in the cupboard is around 18c - 20c, fairly consistently.
Is this how the airlock should function? Am I suppose to leave one side empty and have the other half full? Or do I need to keep topping it up with water every 6-8 hours or so?
Thanks for any help you can provide.