Dyke-builder left rubbish (5)
I believe the answer is:
offal
'rubbish' is the definition.
(I've seen this in another clue)
'dyke-builder left' is the wordplay.
'dyke builder' becomes 'offa' (I've seen this before).
'left' becomes 'l' (common abbreviation).
'offa'+'l'='OFFAL'
(Other definitions for offal that I've seen before include "Bits of waste meat" , "Waste parts of a carcass" , "Waste of carcase" , "Liver, lights, etc" , "Liver, kidney, etc, as food" .)