The most common and most likely answer to this crossword clue is the 5 plus 3 letter word WHOLE HOG
I've seen this crossword clue in The Daily Telegraph
W
H
O
L
E
H
O
G
Buddy explains!
The straight part
We know that "The lengths a complete swine will go to?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case the lengths a complete swine will go to? = whole hog.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.