### Clue: Unusually hardy conservationists in main outlet (7)
### Answer: HYDRANT 
 ### Explanation: Definition: main outlet
 **Anagram of**(Unusually) HARDY + NT(abbrev. for the National Trust for Places of Historic Interest or Natural Beauty, in full, the conservationist organisation in the UK).
Defn: An upright pipe serving as an outlet from the main pipe.