Doctor again involved on a point of sanitation (8)
I believe the answer is:
drainage
'sanitation' is the definition.
The answer and definition can be both acts as well as being singular nouns.
Maybe you can see an association between them that I can't see?
'doctor again involved on a point' is the wordplay.
'doctor' becomes 'dr' (abbreviation).
'involved' is an anagram indicator (involved can mean confusing or complex).
'on' indicates putting letters inside (as in clothing 'on' a person).
'a point' becomes 'e' (compass point).
'again' anagrammed gives 'ainag'.
'dr' put inside 'ainag' is 'drainag'.
'drainag'+'e'='DRAINAGE'
'of' acts as a link.
Can you help me to learn more?
(Other definitions for drainage that I've seen before include "Evacuation -- gardenia (anag)" , "Drawing off liquid" , "Water run-off system" , "Means of discharging water" , "System to manage waste water" .)