The most common and most likely answer to this crossword clue is the 10 letter word UNHYGIENIC
I've seen this crossword clue in The Guardian
U
N
H
Y
G
I
E
N
I
C
More clues leading to the result UNHYGIENIC
Buddy explains!

The straight part
We know that "Insanitary" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case insanitary = unhygienic.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 UNHYGIENIC mean?
UNHYGIENIC adjective- Lacking hygiene; unclean.