The most common and most likely answer to this crossword clue is the 6 letter word QUAICH
I've seen this crossword clue in Financial Times
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Buddy explains!

The straight part
We know that "shallow drinking vessel" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case shallow drinking vessel = quaich.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
Crossword Answer definitions
QUAICH noun- A traditional shallow, two-handled cup of Scottish origin symbolizing friendship. It was originally used to toast the arrival or departure of a visitor.
- (by extension) Any two-handled drinking vessel or trophy.