The pope of trash, the prince of puke, the ayatollah of crud – in his 50-year career, film director John Waters has accrued an enviable array of hideous honorifics, all worn with pride. He is best known for his seminal countercultural comedies, each of them – from Pink Flamingos to Hairspray to Serial Mom – celebrating delicious deviance and alternative family values. His last feature was 2004’s A Dirty Shame and, though he’s still interested in film-making (a new feature, Fruitcake, has been seeking funding for a while and a sequel to Hairspray was commissioned by HBO but not produced), Waters remains sanguine about the forms he works in.

“I just tell stories,” he tells me over the phone from Baltimore, his home town and geographic muse. “It doesn’t matter how.” Waters has increasingly focused on art and writing – a major retrospective has just opened at Baltimore Museum of Art and a new book, Mr Know-It-All, is out soon – and on live performing. That’s the reason we’re talking: Waters brings his one-man show, This Filthy World, to Liverpool this weekend as part of Homotopia, the city’s LGBT+ arts festival.

This Filthy World combines career highlights, anecdotes, opinions and audience interaction. Waters has been touring the show for nearly 15 years to crowds ranging from gay devotees to rock festivals, horror fans to law librarians. The title hasn’t changed but Waters is quick to point out that, even compared to just a few years ago, “there’s [only] one line in it that’s the same. It is a show that I’m constantly updating. I try to make it filthier and dirtier.”

The fun of filth … Divine in Waters’ 1972 film Pink Flamingos. Photograph: Everett Collection/Rex

The world, after all, has changed a lot. These days, LGBT+ visibility is often linked to participation in mainstream institutions such as marriage or the armed services rather than radically distrupting them. Today, if you wanted an equivalent to Pink Flamingos’ contest to nominate the filthiest person in the world, you could look at the Republican party. In other words, gay people pursue respectability while politicians cultivate outrage. “I know,” Waters says. “In my art retrospective, I have a child stroller decorated with the logos of the sex bars of the 70s, like the Hungry Hole and the Stud. That kind of sums it up: those same neighbourhoods are now full of gay people with children.”

Political life in the US, meanwhile, is increasingly fractious. “There’s a civil war in this country right now. But I try to listen to everybody. I’m against separatism – that’s my main message. I try to understand unfathomable behaviour and talk about people we don’t agree with. That’s why every day I read the Wall Street Journal’s editorials. I want to read how smart people I don’t agree with think.”

Waters even reports nattering with the late alt-right tub-thumper Andrew Breitbart. “When we both did the Bill Maher TV show, I hung out with him – this will make the other liberals go crazy – and he said, ‘I do the same thing as you. I copy Abbie Hoffman” – the hippie anarchist. “We’re just on opposite sides doing the same thing.’ And, in a way, he was right.” So, while This Filthy World contains plenty of “anti-Trump stuff”, in Waters’ words, he also invites pro-Trump jokes from the audience. So far there’s only been one taker, “and he was drunk and said, ‘I hate Native Americans.’ I said, ‘Even Trump would hate you.’”

Getting people to laugh is the only way you get anyone to change their opinion John Waters

Waters attributes his lengthy career to his consistently singular sensibility and the bottomless resource of human absurdity. “I don’t think I’m ever mean-spirited and I try to understand human behaviour even though it’s impossible,” he suggests. “Audiences never get mad at what I say. And I try to push the line! I make as much fun of gay political correctness as I do of Republicans. My whole message is don’t judge other people, but at the same time we can’t lose our sense of humour.”

So, while insisting on the value of “comic anarchy” to “wage a war to use wit and humour against our enemy”, Waters also wants to acknowledge that “diversity is quite complicated these days. One of the other Homotopia performers I’m looking forward to meeting is Travis Alabanza, a poet and performer who critiques parts of the feminist community for transphobia. These areas are incredibly interesting but also so complicated that it’s humorous to me” – not the struggle of transgender people, he adds, but the complexity of the dynamics.

Equal-opportunity satire is an admirable aspiration. It’s a shame, then, that at least in our conversation, Waters’ gags at the expense of the left are based more in reproducing conservative stereotypes and canards than in identifying genuine tensions or contradictions in progressive positions. For instance, he singles out the idea of raising children without imposing binary gender expectations – a version of the kind of radical queer experimental living defiantly championed in much of his work – as ridiculous.

“People have babies now and they won’t tell them what sex they are and let them decide! That invites either derision or parody. I understand transgender rights, I’m not saying anything [against them], but I think you do have to tell your children something.” When I ask why he believes this and what conceivable consequences concern him, Waters merely scoffs: “Maybe they’ll be asexual! No, not asexual, what is it? Autosexual! That’s a new militant group that believes masturbation is the only sex they should have and when they have sex with other people, they feel that they have been unfaithful to themselves.”

‘I love Quentin’ … Tarantino’s Once Upon a Time in Hollywood stars Leonardo DiCaprio. Photograph: Trf Images/Rex/Shutterstock

When I ask whether he thinks critical thinking is on the wane, Waters mirthfully reproduces complaints about life getting harder for horny men (“It’s a tough time to ask for a date!”) and straw-man ideas about “what women say” (that innocent men being convicted of sex crimes is acceptable “collateral damage”) or that “in some circles it’s politically incorrect to laugh at anybody”. Waters’ own position, he insists, is that “getting people to laugh is the only way you get anyone to change their opinion. Standing on a soapbox and preaching is not going to change anybody’s mind. Every serious subject I think you can have fun with.”

That said, Waters marks one subject as out of bounds for fun: the repercussions of the Manson family murders, a subject he has engaged with in various ways throughout his career. Waters has long campaigned for the release of his friend Leslie Van Houten, whom he got to know years after her conviction and incarceration as a teenage member of Manson’s cult. Van Houten has served a life sentence but repeated parole recommendations have been refused by political fiat given the case’s continued notoriety.

“She is now an almost 70-year-old woman that looks back with complete horror on what she did, and takes full blame for it, too,” Waters says. The Manson murders will receive more attention next year, their 50th anniversary, not least because they feature in Quentin Tarantino’s forthcoming film, Once Upon a Time in Hollywood. “Quentin is my friend,” Waters says. “I love him, I think he’s a great film-maker, I hope he’ll make a great movie. Will it help [Van Houten]? No movie can really help her because it just reminds people over and over and over. Just be glad your kid never met Manson.” To Waters, the subject fascinates because it offers “a question that there is no fair answer to. What is the humane way to deal with it? That’s what all my work is about.”

And that work is played out, of course, in the key of trash. At the Homotopia festival, Waters previously presented a trash masterclass based on the 1968 schlock classic, Boom! Can he suggest any recent examples of great, fresh trash? “There was a great movie I saw called Mom and Dad, with Selma Blair and Nicolas Cage, about what if everybody in America just started killing their children,” he says. “Hilarious! There’s no such thing as sexploitation films any more, really, though Harmony Korine came close with Spring Breakers. Maybe The Human Centipede was the last one.” The end of an era? “There were a lot of endings in that movie…”

• John Waters: This Filthy World plays as part of Homotopia LGBT+ arts festival at Liverpool Philharmonic Hall on 10 November.