Continue walking along the walkway. Up ahead, Wheatley will move a chamber into your path. Put a portal on the white railing in front of you, then look up through the metal ceiling and put a portal of the other color on the white ceiling in that room. Go through the portals.
Wheatley will send down a bunch of turrets, but fortunately they are all the defective turrets, so they can't do anything. Go through the exit door, which keeps opening and closing over and over.
Out on the walkway, drop down to the walkway down below and go toward the exit door. Up ahead, Wheatley will put some real turrets in the area that you need to go past. There's a light funnel back there. Put a portal where the funnel is shining, then put a portal of the other color on the back wall so it picks up a turret. Wait for the turret to be pushed into the other room, then move the portal so the turret falls. Repeat this with the other turrets.
Now make sure that the light funnel is still flowing toward the other area. Go over to the funnel and jump up into it. Before you reach the wall, walk out of the funnel, because Wheatley opens up a spinny blade wall that will kill you if you don't get out.
Go through the emancipation grill, then put a portal under the light funnel, and put another at the base of the white wall that is across from the open door. Make sure you remember what color the portal in the wall is. Get into the funnel.
When you see a white wall appear up ahead, put a portal in it of the same color as the one you put in the wall earlier. You'll fall into the funnel below, safe from Wheatley's mashy spike plate. When you reach the wall, walk out of the funnel downward to end up on the ledge below. Look to the side to see an escape path. Walk along there to reach a door at the end.
Past the door, a blue gel tube will fall, splattering the walkway with blue gel. Jump from the gel to reach the walkway across the way. Continue walking along until you see a huge number of turrets up ahead. Look for a white ceiling above some glass. Make a portal there, then go back and make a portal on a white wall that you can walk into. Go through.
Walk just past the red button so you can put a portal onto the big white wall next to the turrets. Then stand on the red button and put a portal of the other color under the dripping blue gel in your part of the room. Keep changing the position of the portal on the big white wall until you have disabled all of the turrets.
Create a portal on the angled white wall hanging down where there are some robot arms twitching. Put a portal of the other color on the floor below you. Walk onto the catapult. Take the walkway to the exit door.