Is “There is no sewer one isn’t willing to swim in for one’s master” a popular expression?
Solution 1:
It's not an English idiom, established or otherwise.
If you can't find a phrase via Google (other than extracts from the book and now this question) or in any dictionaries, then it's a very safe bet that it isn't an established idiom. I also couldn't find anything similar in Google Books.
Solution 2:
Not where I live. Probably just an Archerism.