This is the critter spray gun.
The liquid in the jar is at atmospheric pressure (there's a vent hole connecting it to the atmosphere). A fast jet of air flowing right over the end of the pickup tube sucks the liquid up the tube and into the air stream. How exactly does this fast stream of air creates suction? It's released in the atmosphere, so shouldn't it also be at atmospheric pressure?
This is called an aspirator pump. By blowing a jet of air across the top of the dip tube, a slight negative pressure is developed there and the air in the end of the dip tube is thus urged to join in the flow. This draws fluid up the tube which then gets dispersed into the jet.
I can tell you what the answer is:
Please take a look at the first picture. This is the nozzle I provided. The nozzle position should not be high, but relatively low. The straw should enter the main flow of the airflow sprayed by the nozzle.
Then let's take a look at the second picture, which is a partial view of the spray gun.
The blue curve represents the actual path of airflow passing through the top of the straw.
Let's look at the top of the straw again, the red line segment represents the top of the straw.
What is the relationship between this top and the airflow represented by the blue line? This is similar to the relationship between the surface of a wing and the airflow. This is also similar to the relationship between kites and wind. They have an angle. This is similar to the angle of attack of a wing. Due to this relationship, a low pressure will be generated in the upper part of the red line segment. A pressure lower than atmospheric pressure. So the water in the bottle will be sucked up.
So, the reason for the low pressure generated by the spray gun is similar to that of wings and kites.
So why does this relationship create low pressure? Please see this link:
