The most common and most likely answer to this crossword clue is the 9 letter word SOFT-SOAP
I've seen this crossword clue in Financial Times
S
O
F
T
-
S
O
A
P
Buddy explains!
The straight part
We know that "Flannel" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case flannel = soft-soap.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 SOFT-SOAP mean?
SOFT-SOAP noun- Persuasion by means of flattery or pleasing words.
- To attempt to persuade by flattery or pleasing words; to butter up.