I drink bottles - he might benefit from higher 7 21 (6)
I believe the answer is:
waiter
'i drink bottles he might benefit from higher 7 21' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'he might benefit from higher 7 21' is the wordplay.
I cannot quite see how this works, but
'he' could be 'waite' and 'waite' is found in the answer.
A single letter 'r' remains which might be clued in a way I don't understand.
This may be the basis of clue (or it may be nonsense).
(Other definitions for waiter that I've seen before include "Restaurant staff member" , "Restaurant worker" , "Restaurant employee" , "Server in restaurant" , "Estragon or Vladimir, for example" .)