Purple Helen is correct (these are of course the words of Miss Marple - who gets results by having an intensely suspicious mind, always ready to see the worst in everything).
"Sink" in this case doesn't refer to a kitchen basin, but to the archaic English word for a soakaway hole for sewage (i.e. cesspool) - hence "one predisposed ... to put a filthy construction on whatever drains into it".
Thesaurus of traditional English metaphors: "mind like a sink" http://books.google.co.uk/books?id=7JMOAAAAQAAJ&pg=PA379&lpg=PA379&dq=%22mind+like+a+sink%22&source=bl&ots=L1jlo5q1Jr&sig=vsnkoZzUiNbNUTE47XXtPKCY-6c&hl=en&ei=sjPjSf3BCYOhjAeslK3UDQ&sa=X&oi=book_result&ct=result&resnum=5
· 1 decade ago