This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
瀴 combines 氵 (water) with 嬰, which likely contributes the sound. The exact historical development is uncertain.
The left side is water 氵, and the right side 嬰 suggests a complex shape. Without a clear meaning, picture deep water hiding an intricate object.
For エイ, imagine an 'A' floating on deep water: A -> エイ, and the water is deep and unclear.