melt, be charmed, captivated
盪 centers on a state of being softened or moved: melting physically, or being emotionally charmed and captivated as if one's heart has melted.
盪 combines 湯 (hot water) with 皿 (dish), suggesting melting or softening by heat in a vessel. The emotional senses of being charmed or captivated likely extend from the idea of being softened or moved.
Hot water (湯) in a dish (皿) melts whatever is placed inside. Imagine your heart melting like that, leaving you charmed and captivated.
For トウ, picture a toe melting in hot water: toe -> トウ, and the dish catches the melted drops.