Father knocked back a quick drink with the regulars (7)

'the regulars' is the definition.
(I've seen this in another clue)

'father knocked back a quick drink' is the wordplay.
'father' becomes 'pa' (pa can mean dad or father).
'knocked back' says the letters should be written in reverse.
'a quick drink' becomes 'snort' (I've seen this before).
'snort' in reverse letter order is 'trons'.
'pa'+'trons'='PATRONS'

'with' is the link.