Requests bottles to be emptied of fluid (4)
I believe the answer is:
asks
'requests' is the definition.
('ask' can be a synonym of 'request')
'bottles to be emptied of fluid' is the wordplay.
'bottles' becomes 'ampules' (ampule is a kind of bottle).
'to be emptied' means to remove the middle letters.
'of fluid' becomes 'ks' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'ampules' with its middle removed is 'as'.
'as'+'ks'='ASKS'
Can you help me to learn more?
(Other definitions for asks that I've seen before include "is curious" , "Requests information about" , "Demands (something of someone)" , "Poses a question" , "Begs" .)