Swelled, one pulled from drain, exhausted (7)
I believe the answer is:
trebled
'swelled' is the definition.
The definition and answer can be both related to change as well as being past participle verbs.
Perhaps you can see an association between them that I can't see?
'one pulled from drain exhausted' is the wordplay.
'one' becomes 'i' (Roman numeral).
'pulled from' indicates named letters should be taken away.
'drain' becomes 'tire' (tiring is a kind of draining).
'exhausted' becomes 'bled' (to exhaust something might be to bleed it dry).
'tire' with 'i' taken away is 'tre'.
'tre'+'bled'='TREBLED'
Can you help me to learn more?
(Other definitions for trebled that I've seen before include "Increased threefold" , "produced twice as much again" , "Multiplied by three" .)