How do bucket/saucer waterers work?

[Mrs. Mucket]

Just curious, does someone have a simple (not-too-scientific

) explanation for how the bucket/bottle + saucer waterers operate? Is it some kind of a siphon effect?
I have made two small ones that seem similar--each has one small hole below the saucer lip level and I plug the hole while filling. The bucket with 6" lid won't work unless the lid is sealed. The water bottle with 1-1/2" cap won't work unless the cap is loose. Why the difference?

 

[catdaddy66]

The bucket waterer needs to have its holes near the TOP where the lid is attached (screwed with my head at first, too). When full, replace lid and turn over into the tray...once the fluid reaches the level of the holes, the water stops flowing. Similar to the way a straw holds fluid w/ your finger over the top to create suction. That is why the lid needs to be on for it to work. Hope that helps!