What does it mean by "a mind like a sink"?

This is from a novel.

As I've told you, I've got a very suspicious mind. My nephew Raymond tells me in fun, of course, that I have a mind like a sink. He says that most Victorians have. All I can say is that the Victorians knew a good deal about human nature.

Thank you very much
Update: Purple Heaven, thank you. I got it.
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