Smutty material: this should be cleaned up! (5)
I believe the answer is:
'smutty material' is the definition.
(I've seen this in another clue)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for filth that I've seen before include "Real dirt or obscenity", "Disgusting dirt or obscenity", "Dirt, obscene talk", "Repulsive dirt", "Squalor".)