There is a catapult in front of you, then another on the far side of the room. Between the two catapults, there is a white floor. Put a portal on the wall across from the funnel, then put another on the white floor between the catapults to make the funnel come out between the catapults.
When you are up on the ceiling, look at the color of the portal below you. Make a portal of the other color on the angled piece of wall facing the small red button on the far side of the room. When you fall into the portal below you, you'll be thrown over to the small red button.
Before you press the small red button, put a portal on the wall across from the funnel and another portal on the floor between the two catapults like before. Then press the red button. The frankencube will land on the catapult and end up inside of the funnel. Put a portal on the angled wall to make the frankencube fall into the portal below it and out of the angled wall to where you are standing. Be ready to catch it when it comes your way, because otherwise it may bounce off of the wall and fall into the pit. Put the frankencube on the big red button then go through the exit door.