I'm doing this from memory, as I no longer have the 2002 ZX5 that this applies to.
I recall that each side of the sunroof has a hose that runs down the B pillar (or possibly the A or C pillars), into the rocker panel area. From there it is *supposed* to go through a hole in the frame, so that it empties directly onto the ground.
On my car, the passenger side worked this way. However, on the driver's side, the hose had fallen back through the hole in the frame, causing it to empty inside the rocker panel instead. As a result, my driver's side rocker panel rusted out.
The proper cure is to fish the end of the drain hose back through the hole in the frame, so that it empties directly onto the ground. The problem is that the hose is a bit shorter than it should be, so it may have a tendency to fall back through the hole, and then drain into the rocker panel again.
Fish the drain hose through the frame hole with a stiff wire (bent-up hanger), and then seal up the hole with some sort of caulk or sealant, so that the hose can't fall back through the hole. Good luck!