Possible need for invalid inferior writer switching contents (6)
I believe the answer is:
bedpan
'switching contents' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.
'possible need for invalid inferior writer' is the wordplay.
I cannot quite understand how this works, but
'writer' could be 'ed' (I've seen this in other clues) and 'ed' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
(Another definition for bedpan that I've seen is " Hospital receptacle".)