The sailor, to have a puff, goes back outside (3,3)
I believe the answer is:
sea dog
'the sailor' is the definition.
(sea dog is a kind of sailor)
'a puff goes back outside' is the wordplay.
'a puff' becomes 'ad'.
'back' says the letters should be written in reverse.
'outside' means one lot of letters goes inside another.
'goes' back-to-front is 'seog'.
'ad' going into 'seog' is 'SEA-DOG'.
'to have' is the link.
(Other definitions for sea dog that I've seen before include "'Old salt (3,3)'" , "Experienced sailor (colloq.)" , "mythical creature" , "Old or experienced sailor" , "Dosage (anag)" .)