All-plastic atmospheric column type poultry water dishes.
To fill, invert and remove base. Reattach base and set right way up. Air pressure supports the water column. As water is taken from the dish, air enters the chamber and water is let out.
These drinkers have the added feature of a carry-handle incorporated. This entails not just a handle, but a more complex dish-attachment mechanism, which enables the drinker to be easily lifted and moved, without coming apart or losing water. Well worth the extra cost if you need to move the drinker regularly.
Note: These drinkers are not UV resistant. Try and keep out of direct sunlight.