The most common and most likely answer to this crossword clue is the 12 letter word BOOT-CATCHER
B
O
O
T
-
C
A
T
C
H
E
R
Buddy explains!
The straight part
We know that "He helped to keep tavern floor clean" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case he helped to keep tavern floor clean = boot-catcher.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.