How does that PVC waterer work anyways?

[Hatrick]

So after looking at and being jealous of Monk's delightful coop, I want to install the same type of waterer in our small coop, but I don't understand how it works.
Is there some type of fitting inside that prevents the water from just flowing out?
You fill it from the top right? If that entire tube is full of water then how is it not coming up and out?
I don't understand.

 

[Stumpy]

I'd love to know the answer, too!

 

[CoyoteMagic]

https://www.backyardchickens.com/forum/viewtopic.php?id=194306&p=1

Have you checked out this thread? It's all got to do with air pressue/vaccum and all that scientific stuff. It's really easy.