Is there a trick I'm missing to adjust water levels in the Little Giant 2500-series poultry founts? Per the instructions, screwing the control nut toward the spring increases water level; screwing it away from the spring reduces. Clear and simple. Except that there seems to be an imperceptible microfraction of a turn between a damp puddle in the bottom of the bowl, and overflowing enthusiastically onto the ground. What am I doing wrong? The fount is brand new. Could the valve be defective?