Charles Bukowski — a gutter laureate who wrote beautifully and frankly about drinking, fighting, women, horse racing and most every aspect of life’s underbelly — has been dead for 25 years as of this month.

But, by all indications, his passing has done nothing to hurt his output.

More than a dozen collections of old poems and letters have been published since the death of Bukowski. But those works have been rightfully criticized as second rate (there’s a reason they weren’t released when Bukowski was alive). Hence, it is his older poems, short stories and novels — which inspired the movies “Barfly” and “Factotum,” starring Mickey Rourke and Matt Dillon, respectively — on which the hard-living Bukowski’s reputation and collectibles market are built.

First-edition books with paintings by the man whose job in a post office inspired his first novel in 1971, easily go for $5,000. And while every Bukowski fan has read all of his classic output, something new and intriguing and unexpected has hit the market. Now, a well-heeled Bukowski devotee hungering for a first-time read of peak work by the author — who made ends meet through writing fiction for so-called skin-magazines such as Hustler and Cavalier — can get that opportunity.

The price tag is $27,500 and the story is one that even Larry Flynt found too obscene for publication.

Entitled “The Hog,” Bukowski’s manuscript (complete with pencil edits by the author) comes bundled with a couple dozen letters written by him to former High Times editor Larry “Ratso” Sloman. The whole thing is offered, by rare book dealer Ed Smith, in a box made of pigskin and branded in front with a drawing by Bukowski.

“I was excited to see this,” Smith tells The Post. “Every big Bukowski collector who thinks he has everything, well, he doesn’t have this. And the letters give the background to make it all believable.”

The story inside the pigskin box involves a perverse elderly millionaire, his erstwhile major-domo, a teen prostitute and a hog named Harry Truman. Things end badly for the hog and the hooker — and bestiality isn’t the only taboo broken in the telling of the tale. Nevertheless, says Smith, “Who knows? Bukowski’s wife [who oversees his estate] might have something 10 times worse than this.”

The story is out-there enough that Bukowski knew his longtime editor/publisher John Martin wouldn’t touch it. “We spoke right after he sent it to me,” Martin says. “The first thing he said was, ‘I know. You’re not going to publish it.’ ” Martin believed that Bukowski was better than the material and did not think it would do much to help his reputation.

Smith, who believed that Ratso’s copy of the manuscript was the only one remaining in existence (that is actually incorrect), speculates that Martin may have burned his version in a fit of pique. Martin says that this is not so, although he is not sure that “The Hog” made it into his archives, which were sold to UC Berkeley.

The bigger question resides in how the story came to be in the first place.

Martin has his version of events: “This guy named Ratso asked Hank [the name by which everybody called Bukowski] to write the dirtiest story he could.” According to Martin’s telling — which presumably came directly from Bukowski — he honored the request, but High Times would not publish it. “Of course I wound up not publishing it either. If it’s too hot for Ratso, it’s too hot for me.”

Ratso, who sold his copy of the story and the letters to Smith through a dealer for somewhere between $10,000 and $20,000, laughs at this telling of events.

“That’s ridiculous; I would never say that to him,” says Ratso, who’s out of the magazine business, but writes books (including co-authoring two with Howard Stern) and will be releasing an album that includes a duet with Nick Cave on April 5th.

“Bukowski said to me, ‘I don’t know if you have the guts to publish this, but I want to send you [a story].’ It was ‘The Hog.’ He was doing a column for us and I didn’t keep copies of the stories we published. I worked on them and sent them to copy edit. But this one, they gave back to me [because it wasn’t going to be used] and I kept it. I thought in the back of my mind that it might be valuable someday.”

As for the content, and the reason it has never been published, Ratso says, “bestiality is the least of it.”

I can attest to that assessment. I, too, have a copy of “The Hog.” Mine was obtained during an early job working as an editor for Oui magazine, which was launched by Playboy in the 1970s and sold to a bottom-of-the-barrel publishing company, presumably with the intent of putting the magazine out of its misery (a ploy that worked). While there, I, too, hired Bukowski to write an ongoing column, which was called Dreams of the Beast. In late 1982 or early ’83, Bukowski sent me the unpublishable story.

Under circumstances similar to those of Ratso, I hung onto my copy.

So now, according to book dealer Smith, there are currently two versions in existence. As to whether or not the legendary story will ever see the light of the day, Ratso opines, “Are you crazy? It’s completely unpublishable — especially if animals get their #MeToo movement.”