The blue line and arrow is the path of the air that is sucked in from the vacuum port. It enters the chamber above the Flap Valve. (Underneath from this view because the tank is upside down.) This is the #1 Preps of iRobot's diagram for the Scooba.

The Red lines with arrows is the air path from the #4 Dries of iRobot's diagram.

The Yellow line is the air that is being sucked into the Filter screen. From there, it goes to the suction fan and is then exhausted from the Scooba by the left wheel. Some of the air is also diverted to the #1 Preps to blow dirt towards the vacuum port.