Greek father is up and down for a drink (6)
I believe the answer is:
grappa
'a drink' is the definition.
(grappa is a kind of drink)
'greek father is up and down' is the wordplay.
'greek' becomes 'gr' (abbreviation for Greek).
'father' becomes 'pa' (pa can mean dad or father).
'is up' says the letters should be written in reverse (in down clue: letters go upwards).
'and' says to put letters next to each other.
'down' becomes 'pa' (I am not sure about this - if you are sure you should believe this answer much more).
'pa' reversed gives 'ap'.
'gr'+'ap'+'pa'='GRAPPA'
'for' is the link.
(Other definitions for grappa that I've seen before include "Spirit distilled from grapes" , "Brandy from fermented pressed grape residue" , "Italian spirit made from grape residue after pressing" , "Italian drink" , "Form of brandy" .)