The most common and most likely answer to this crossword clue is the 8 letter word BUCKWASH
B
U
C
K
W
A
S
H
Buddy explains!
The straight part
We know that "old bleaching process (" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case old bleaching process ( = buckwash.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.