jar
甒 centers on a type of container: a jar, specifically an earthenware vessel used for holding liquids or food.
甒 combines 瓦 (earthenware) with 無, which likely contributes the sound. It originally referred to a specific type of jar or vessel.
The left side 無 suggests emptiness, and the right side 瓦 is earthenware. Picture an empty earthenware jar waiting to be filled.
For ブ, imagine a jar with a label that says 'Boo!' — a playful ghost hiding inside: Boo -> ブ.