heron, small cup
雚 centers on a tall wading bird, the heron, and by extension a small cup, likely from a shape association with the bird's slender neck or bill.
雚 is a pictograph of a heron-like bird, with the top 艹 suggesting the bird's crest or the reeds it stands among, and the lower part 隹 representing the bird's body. The small cup meaning may derive from a separate phonetic loan or a shape analogy.
The top 艹 looks like reeds, and the lower part 隹 is a bird. Picture a heron standing tall among the reeds. The small cup meaning can be remembered by imagining the heron's long bill dipping into a tiny cup of water.
For カン, imagine a heron holding a small can in its bill: can -> カン, and the heron is using the can as a tiny cup.