I missed that you were looking at the rear... The shop manual diagnosis chart is below, the helpful bits say to pull the headliner and check the hoses and that it does route through the C pillar as you guessed.. I still can't locate where the rear drain tubes exit though, if someone else knows offhand please chime in. I'll look some more for a diagram later this weekend if you don't have an answer by then.
Edit: Have you pulled the c-pillar trim? With the headliner pulled back, it sounds like you're close to being able to trace the line all the way down.
B5 CHECK THE DRAIN HOSES
NOTE: Drain hoses can be viewed with a flashlight by removing the headliner lace around the inside opening and gently pulling down on the headliner. (On some vehicles, Velcro style attachments have been installed in place of the trim lace.)
- Make sure the drain hoses are all connected and not cracked, slit, pinched or obstructed.
- Are all the drain hoses present and attached correctly?
Yes
GO to
B6 .
No
REPAIR or INSTALL a new drain hose(s). TEST the system for normal operation.
B6 CHECK THE DRAIN HOSES FOR CORRECT FLOW
NOTE: Drain hoses must flow downhill and cannot be pinched or restricted by headliner or any other trim components.
- With the panel in the open position, slowly pour water into the water trough area and make sure that the same amount of water exits the vehicle at the bottom of the A- and C-pillars.
- Check the drain hoses for obstructions by blowing compressed air through the drain spouts in the water trough area, then retest the water.
- Are the drain hoses operating correctly?
Yes
INSPECT other areas of the vehicle that may cause water to enter the roof area, such as, the windshield or luggage rack if equipped. If no concerns are found, GO to
B7 .
No
Lower the headliner and INSPECT the drain hoses for correct routing. REPAIR or INSTALL a new drain hose(s). TEST the system for normal operation.