Tippling eggnog to begin with, Everyman returned to chuck it down (4)
I believe the answer is:
teem
'chuck it down' is the definition.
(teem can mean to rain)
'tippling eggnog to begin with everyman returned' is the wordplay.
'to begin with' suggests taking the first letters.
'everyman' becomes 'me' (where the crossword setter is 'Everyman').
'returned' is a reversal indicator.
The first letters of 'tippling eggnog' is 'te'.
'me' reversed gives 'em'.
'te'+'em'='TEEM'
'to' is the link.
(Other definitions for teem that I've seen before include "Bear" , "Swarm around meet" , "Come down hard" , "Be prolific" , "Flow copiously" .)