The most common and most likely answer to this crossword clue is the 7 letter word GUSHERS
I've seen this crossword clue in The Guardian
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More clues leading to the result GUSHERS
Buddy explains!

The straight part
We know that "who can be very talkative" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case who can be very talkative = gushers.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.
What does GUSHERS mean?
GUSHERS noun- One who gushes (makes an excessive display of enthusiasm, praise, or sentiment).
- An oil well that has a natural flow and so requires no pumping.