drain
釂 centers on draining a vessel completely, especially drinking every last drop. The single given meaning 'drain' captures this idea of emptying a container of liquid.
釂 combines 酉 (wine vessel) with 爵 (a type of ritual wine cup), suggesting the idea of draining a cup of wine. The exact historical development is uncertain, but the component choice strongly points to finishing a drink.
The left side 酉 is a wine jar, and the right side 爵 is an ancient wine cup. Picture someone tilting the cup and jar until every last drop is drained.
For ショウ, imagine a show-off at a banquet draining his cup in one go to impress everyone: show -> ショウ, and the wine disappears.