Old Zulu enters South African watering hole (6)
I believe the answer is:
boozer
'watering hole' is the definition.
(both can informally mean a pub)
'old zulu enters south african' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'zulu' becomes 'z' (phonetic alphabet: alpha, bravo, charlie etc.).
'enters' indicates putting letters inside.
'south african' becomes 'boer' (Boer is an example).
'o'+'z'='oz'
'oz' put into 'boer' is 'BOOZER'.
(Other definitions for boozer that I've seen before include "Pub (slang)" , "Pub (sl.)" , "Inn" , "Heavy drinker" .)