For sucking to work, the whole rear of the newt needs to be enclosed with the only escape via the fan, else the fan will just suck air from next to fan outside the tube and have absolutely no effect.
You can test this by putting a fan in front of your face blowing awau from you and feel the wind rushing past your ears as it suck the air past you into the nearby room.
Now do the same test above with a 1m cardboard tube place against the rear of the fan and put your face up close to the tube.