Rob can start to tire (4)
I believe the answer is:
'rob' is the definition.
(loot can mean to rob)
'can start to tire' is the wordplay.
'can' becomes 'loo' (both can informally mean toilet).
'start to' indicates taking the first letters.
The first letter of 'tire' is 't'.
(Other definitions for loot that I've seen before include "Swag, booty" , "Stolen goods" , "Booty, spoils" , "Orton play; ill-gotten gains" , "Booty; sack" .)