Fish stuck in waste trap (5)
I believe the answer is:
tetra
'fish' is the definition.
(tetra is a kind of fish)
'stuck in waste trap' is the wordplay.
'stuck in' indicates a hidden word.
'TETRA' is hidden in the letters of 'waste trap'.
(Other definitions for tetra that I've seen before include "Brightly coloured aquarium fish" , "Denoting four (prefix)" , "Bright tropical fish" , "This indicates a group of four" , "in groups of four" .)