It’s full of patient customers (8)
I believe the answer is:
hospital
'of patient customers' is the definition.
The definition suggests a singular noun which matches the answer.
'it's full' is the wordplay.
I cannot really see how this works, but
'it's' could be 'it' (I've seen this in other clues) and 'it' is present in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for hospital that I've seen before include "Medical centre" , "asylum?" , "Treatment and care centre" , "Spoil hat (anag)" , "Possibly Guy's" .)