It’s no secret that New York’s pols are expert at plucking campaign cash seemingly from thin air – but kudos (of sorts) to Brooklyn City Councilman Bill DeBlasio for a particularly deft display of the craft.

As The Post reported yesterday, DeBlasio – who’s running for public advocate – recently criticized what he termed an “unreasonable crackdown” by the Department of Buildings on illicit outdoor advertisements.

Ka-ching!

In just days, his campaign bank account accrued a cool $8,000 in donations from . . . ta da! . . . billboard companies.

And that’s how that game is played, boys and girls.

To be sure, $8,000 isn’t a whole lot of money. (Then again, public advocate isn’t a very important job, either; calling press conferences to declaim “unreasonable crackdowns” and such is just about all an advocate does.)

Still, the speed of the declamation-contribution turnaround in this case was truly impressive.

Moreover, while there’s nothing inherently wrong with campaign contributions – think the First Amendment in action – DeBlasio and his fellow councilmembers have long been prone to self-righteous preening about the role of “corporate money” in politics.

Now we know how much that posture is worth.

Somewhere south of eight grand, to be exact.