Very experienced drunk (6)
I believe the answer is:
soused
'drunk' is the definition.
(sousing is a kind of drinking)
'very experienced' is the wordplay.
'very' becomes 'so' (I've seen this in other clues).
'experienced' becomes 'used' (as in 'used to').
'so'+'used'='SOUSED'
(Other definitions for soused that I've seen before include "Marinated" , "Soaked, pickled (gherkin); drunk (colloq.)" , "Drenched with liquid" , "Drunk or immersed in liquid" .)