to put a coffin in a grave
窆 centers on the act of lowering a coffin into a grave for burial. It is a specific ritual action rather than a broad concept.
窆 combines 穴 (hole, cave) with 乏, which likely contributes a phonetic element. The character is associated with placing a coffin into a burial pit.
The top 穴 suggests a hole or pit, and the bottom 乏 looks like a person bending down to lower something. Imagine a grave pit being prepared as a coffin is carefully lowered inside.
For ビン, picture a coffin being lowered into a bin-shaped grave: bin -> ビン, and the pit receives the coffin.