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When various metal pieces are stamped out at the factory, small indentations are also stamped into them. If you look at the bottom area of the car under the drivers door, for instance the rocker panel, you will see a seam, which is the result after two stamped pieces of metal are welded together. You will also see some areas where the seam appears to have a hole in it from the aforementioned indentation. These are your 'drain holes' and can be found on the doors too. Poke a small rigid wire up these holes but watch for draining water. The manufacturer usually has a water management system relating to these holes. When driving in a rain storm, water will enter the inner sections of the car and drain out farther down, through a drain hole. If the holes are blocked, water will not drain and will slosh around inside the car.

I hope this helps.