Discard in tip (4)
I believe the answer is:
dump
I believe this clue is a double definition.
'discard' is the first definition.
(dumping is a kind of discarding)
'tip' is the second definition.
(I've seen this before)
'in' is the link.
(Other definitions for dump that I've seen before include "Get rid of" , "Rubbishy place" , "Place where rubbish is deposited" , "Unload" , "Offload" .)