Scupper

A scupper is an opening in the side walls of a vessel or an open-air structure, which allows water to drain instead of pooling within the bulwark or gunwales of a vessel, or within the curbing or walls of a building.

There are two main kinds of scuppers:

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Two scuppers cut into either side of this outdoor stairwell prevent water from building up and making the stairs slippery.
Ship's bulwark. 1. Gunwale, 2. Bulwark plating, 3. Flange, 4. Stanchion, 5. Stringer plate, 6. Stringer angle, 7. Sheerstrake. Scupper: 8. hole (with grille cover), 9. pipe, 10. outlet.