First, I apologize if I don't use proper terms. I'm not very educated when it comes to physics. That being said...
I want to make a watering station for my chickens. I have built the attached image.

[![enter image description here](https://i.stack.imgur.com/nFaRC.jpg)](https://i.stack.imgur.com/nFaRC.jpg)

My problem is, when the bucket is filled, lid on, and valve turned on, the water doesn't stop flowing when it goes above the hole I drilled in the downpipe. My assumption was that once the hole was covered, it wouldn't get air to drain, and it would stop. What's more, bubbles come out the bottom.

Assuming the bucket is air-tight, is this because the head pressure is so great it forces itself out or?? That's all I got. I've searched for hours for an answer, without knowing the proper terms to search for, I can't find anything.

Thanks, in advance!

***UPDATE***
The reason I put this valve in is so I can stop flow, take the lid off and fill the bucket without it flowing out of control down to the watering portion. Would a check valve accomplish this, or would it not have enough pressure to work correctly?