The most common and most likely answer to this crossword clue is the 9 letter word JETTISONS
I've seen this crossword clue in The Guardian
J
E
T
T
I
S
O
N
S
Buddy explains!

The straight part
We know that "Dumps" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case dumps = jettisons.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.
What does JETTISONS mean?
JETTISONS noun- (collective) Items that have been or are about to be ejected from a boat or balloon.
- The action of jettisoning items.
- To eject from a boat, submarine, aircraft, spaceship or hot-air balloon, so as to lighten the load.
- To let go or get rid of as being useless or defective.