Toilet observed in a bit as not engaged (2,1,5,3)
I believe the answer is:
at a loose end
'not engaged' is the definition.
I don't know anything about this answer so I cannot judge whether this works.
'toilet observed in a bit' is the wordplay.
I cannot really understand how this works, but
'toilet' could be 'loo' (loo can informally mean a toilet) and 'loo' is found within the answer.
'observed' could be 'seen' (synonyms) and 'seen' is located in the answer.
'a' is present in the answer.
'bit' could be 'tad' (both can mean a small amount) and 'tad' is found within the remaining letters.
This accounts for all the letters.
This explanation may well be incorrect...
'as' acts as a link.
Can you help me to learn more?
(Other definitions for at a loose end that I've seen before include "Without purpose or occupation" , "Twiddling one's thumbs" , "With nothing specific to do" , "idle" .)