The connection is that Manson took a couple classes, left and used some of what he learned to attract people to his family.
As far as I know he's never been declared clear.
Nor has he been embraced by the church, but detractors have been quite eager to link him to them.
That being said, the membership numbers they report include anyone who has bought a book or taken an introductory class, whether they pursued it any further or not.
Manson even had an e-meter at the Ranch.
some references claiming Manson was “clear”
http://www.mansonblog.com/2016/07/lanier-ramer.html
Two sinister Scientology graduates of the 60s were Robert DeGrimston and his wife Mary Ann. He was a former architecture student and she was a former prostitute who believed herself to be Joseph Goebbels incarnate. Both had an insatiable preoccupation with death and violence and it is perhaps inevitable that they ended up in San Francisco in 1967 where they established themselves as The Process Church of the Final Judgement. They took up residence on Oak St., in the so-called Devil House, two blocks from where Charles Manson had his ‘family’ and close by Anton Lavey’s Church of Satan. Processans wandered the Haight sporting black capes and black suits and preaching a gospel of doom and destruction. The first edition of Ed Sanders’ book The Family carries an interesting chapter on the Process Church. But a Chicago lawyer convinced them to sue for defamation and the offending chapter was deleted from subsequent editions. Robert Degrimston published several books on war (his favorite theme) and commanded his followers “THOU SHALT KILL!” Another Process publication urged readers to experience the pleasures of grave robbing and necrophilia. A rant in the ‘Death’ issue of their magazine was penned by Charles Manson. Manson’s rap was an amalgam of Process ideology and the 150 hours of Scientology auditing he’d received during one of his numerous prison stints (Charlie declared himself a ‘Theta Clear’).
Contrary to popular belief, the Process is still around, having undergone numerous name changes over the years. The first was the ‘Four-P Movement.’ Author Michael Newton wrote that the cult, “is also deeply involved in white slavery, child pornography and the international narcotics trade.” Still other name changes for the Process included The Foundation Church of the Millenium, The Foundation Faith of God and then Best Friends Animal Sanctuary. Today it is known as The Best Friends Animal Society and is located in Kanab, Utah. Mary Ann Degrimston makes her home there along with several other former members. Gone are the days when Process members journeyed to San Quentin to interview Manson. Gone too are all references to Satan and doomsday. Members now softpeddle their involvement in the Process Church of the Final Judgement citing juvenile misguidance. The goal of the reformed church now is to save animals. The large compound in southern Utah is their testament to this end. And the animal sanctuary is a huge cash cow. In 2003 the Society raised more than $20 million. Perhaps the Degrimstons were wise to abandon Scientology when they did. Robert currently works in New York City as a business consultant.
Maryann has passed away since this was written.....
https://www.alternet.org/news-amp-politics/he-was-no-hippie-remembering-manson-prison-scientology-and-mind-control
By Paul Krassner / AlterNet November 26, 2017 (Yippie publisher of The Realist)
...When Charles Manson was a prison inmate, he got introduced to Scientology by fellow prisoners, and his ability to psych out people was intensified so that he could zero in on their weaknesses and fears. In 1967, he was released and went to the Scientology Center in San Francisco. A friend who accompanied him there told me, “Charlie said to them, ‘I’m Clear – what do I do now?’”
But they expected him to sweep the floor – shit, he had done that in jail. However, in Los Angeles, he went to the Scientology Celebrity Center. Now this was more like it – there he could mingle with the elite. I was able to obtain a copy of the original log entry: “7/31/68, new name, Charlie Manson, Devt. No address. In for processing = Ethics = Type III.” The receptionist – who, by Type III, meant “psychotic” – sent him to the Ethics office but he never showed up.
At the Spahn Ranch, Manson combined his version of Scientology auditing with post-hypnotic techniques he had learned in prison, with geographical isolation and subliminal motivation, with sing-along sessions and encounter games, with LSD and mescaline, with transactional analysis and brainwashing rituals, with verbal probing and sexual longevity that he had practiced upon himself for all those years in the privacy of his cell. He was also raped by fellow inmates...
...A few months later, when the family members were captured and charged with homicides, Manson was portrayed by the media as a hippie cult leader, and the counterculture became a dangerous enemy. Hitchhikers were shunned. Communes were raided. In the public’s mind, flower children had grown poisonous thorns. But Manson was never really a hippie....
Bernadine Dohrn, Weather Underground terrorist and criminal: “Dig It. First they killed those pigs, then they ate dinner in the same room with them, they even shoved a fork into a victim’s stomach! Wild!”
https://www.cs.cmu.edu/~dst/Fishman/cooper-scandal.txt
One famous, in fact infamous person interested in Scientology
that they do not boast about, talk about, or probably even want
is Charles Manson, the convicted murderer of Sharon Tate and
her friends. The New York Times stated that Manson first got
interested in Scientology while he was incarcerated in the McNeil
Island Penitentiary in Washington (Scientology’ has programs for
prisons). After his release, The Times reported, he went to
Los Angeles where he was said to have met local Scientologists
and attended several parties for movie stars, possibly the July
18 dedication of the celebrity center. Scientology literature
was also said to be found at the ranch when Manson and his family
were captured. But for reasons unknown, it is claimed that Manson
may have been made a “suppressive person” by the Scientologists,
and there have also been hints that he may have joined the Process,
the sex and satan group which originally broke away from Scientology.