This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 缼 is uncertain. It visually combines 缶 and 欠, but the original semantic or phonetic role of these components is unclear.
Since the meaning is unclear, focus on the shape: a can (缶) next to a yawning person (欠). Imagine a can that is missing something, but what it lacks is unknown.
For ケツ, imagine a can (缶) that is missing (欠) its lid, and you say 'kets!' as it pops open. The sound 'kets' cues ケツ.