Body fluid and fly found in mug (8)
I believe the answer is:
pushover
'mug' is the definition.
(thesaurus)
'body fluid and fly' is the wordplay.
'body fluid' becomes 'pus' (pus is a kind of body fluid).
'and' says to put letters next to each other.
'fly' becomes 'hover' (hovering is a kind of flying).
'pus'+'hover'='PUSHOVER'
'found in' is the link.
(Other definitions for pushover that I've seen before include "Something easily done" , "breeze" , "A thing easily done" , "Person easily convinced or deceived - or shoved down" , "Child's play, piece of cake" .)