chem chlorine water problem

Main reason:
Inverted funnel has larger surface contact area than thin tube
So rate of dissolving chlorine is much faster

There is also a not really very important reason
Due to gravity, chlorine will sink if you use inverted funnel
so the gas will itself go to contact with water
But using a thin tube cannot have this effect
The gas can just float to the water, by not by gravity, which is much faster

I hope this can help you!