The most common and most likely answer to this crossword clue is the 8 letter word SEDIMENT
I've seen this crossword clue in The Guardian
S
E
D
I
M
E
N
T
More clues leading to the result SEDIMENT
- Staff in courses on reflection settled matter
- Deposit small amount of money, getting ecstatic about it
- Despatched to find coin in mud
- Deposit posted, money banked
- Waste product generated by people tucking into bad diets
- Ten dimes sent as deposit
- Deposit small coin in tens roughly
- Delivered with money enclosed, matter settled?
- Deposit money in extremely safe organisation managing estates
- Small sum of money sent round as deposit
Buddy explains!

The straight part
We know that "Waste product" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case waste product = sediment.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 SEDIMENT mean?
SEDIMENT noun- A collection of small particles, particularly dirt, that precipitates from a river or other body of water.
- To deposit material as a sediment.
- To be deposited as a sediment.