This unit works very well -- if you have a little common sense. It works only when the black screw top is tight enough to seal the 'O' ring against the white plastic neck. Otherwise, there is no vacuum created and the water can simply run out. A new 'O' ring or a dab of vaseline will help the seal if the waterer is old. If it's new, screw the top down very tightly. As for the cap -- there is a nib on the top edge of the waterer to 'store' the cap when the waterer is in use. The cap is only used when filling the unit. once it is in place the cap is removed and, if the top is screwed on tightly enough, water stops at the top edge of the bottom spigot due to the vacuum effect. Confusion solved? Even "Customer Service" doesn't seem to know how this product works. C'mon folks, it's not rocket science.

The top is next to impossible to unscrew. I have to set on the tank and pry off the top with a pipe. and no i don't tighten it down to much. I close the lid until the water stops pouring out the spout. I have used this watering system for 10 plus years with no problems, but this last batch has me looking else where for waterers.