The most common and most likely answer to this crossword clue is the 7 plus 2 letter word DISPOSE OF
I've seen this crossword clue in The Times
D
I
S
P
O
S
E
O
F
More clues leading to the result DISPOSE OF
Buddy explains!
The straight part
We know that "Dump" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case dump = dispose of.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.