Where are drains located on a 2003 chevrolet impala sunroof?

They go down inside front A pillar an inside rear D pillar . To get at them you need to take trim off an the headliner down .
Sunroof Housing Rear Drain Hose Replacement (Impala)
Remove the headliner. Refer to Headlining Trim Panel Replacement in Interior Trim. Remove the rear quarter lower trim panel. Refer to Rear Quarter Lower Trim Panel Replacement in Interior Trim. Disconnect the rear sunroof drain hose from the sunroof module rear spigot. Remove the tape from the rear sunroof drain hose tube.
Disconnect the rear sunroof drain hose from the rear sunroof drain hose tube. Remove the rear sunroof drain hose tube from the upper retainer clip. Remove the rear sunroof drain hose from the rear pillar
The front is simalier .