They are grabbing that success with both hands, possibly to the detriment of their health. Having toured 1995's self-titled debut album (sales of 4 million and counting) to the point of exhaustion, they are doing the same with their second, Version 2.0, going at it like madmen, because who knows how long this kind of thing can last? If you want to speak to them, you have to hop aboard the tour, so I met them in Atlanta, Georgia.
Atlanta, these days, is full of sweet things; plantations of peaches packed into food and toiletries until the scent makes you gag; the World of Coca-Cola pavilion, famed for six-foot jets of sugar gloop; mansions that should have the theme-tune from Gone With the Wind swelling behind them. It's at odds with what you know about Shirley Manson, whose lyrics - masochism, domination and obsession sung over the boys' grungy, effect- heavy hooks - indicate someone acerbic, if not bitter. Speak to her, though, and it becomes clear that that was last year's model. Manson is the first to admit to her own neurosis, which probably explains the crowd- pleasing exhibitionism that had her posing with her knickers on show just a year ago, or telling one drooling hack that her orange Fender Stratocaster is "the colour of my pubic hair". This explosiveness has quietened down somewhat, and so has the rage and self-hate of early interviews. The band, it seems, has been her Prozac, even in the tour mechanics. "I'm built for this kind of work. I'm a monster, so it exhausts me in the best way. And it's a form of escape - your brain is filled with so much extra-curricular activity, you don't need to think about what's going on between your ears."
It is difficult at first to see where the anguish came from. Though she says she hates her looks, Manson is delicately beautiful, with red hair, auburn eyebrows, and lips big enough to land a plane on. Born and brought up in Edinburgh, she is the middle daughter of a genetics scientist and a mother "gifted with parental skills". School saw the first creak of trouble. Put into a tough comprehensive, she was bullied for her accent and A-grades, called "bloodhound" and "frog eyes". Which may not sound like much, but it left its mark. "Somehow, I attracted the attentions of a very aggressive girl. She got into my mind and f---ed with me big- time. And I don't think you ever get over it, to be honest. My parents claim I made a crucifix, twigs tied together with pink beads, and hung it outside my window with a letter to God, pleading to get rid of this girl from my life. It makes me feel sick now, but at least it shows a semblance of intelligence, a determination for change."
Still, the A-grades disappeared, and Manson left school to work in Miss Selfridge ("my glorious wonder years"), where she specialised in make- up, customer intimidation and beating her head on the wall in frustration. Having been trained in piano, violin and clarinet, she also found herself in a part-time band, the doomy goth-band Goodbye Mr McKenzie. They got signed but nosedived, and Manson gradually developed clinical depression. Trying to relaunch the band as Angelfish, she was bedbound half the time, "immobile, stupefied". Her dole officer fixed up an interview in an Edinburgh pie shop.
Six thousand miles away, the respected producers Butch, Duke and Steve had decided on a mid-life attempt to plot a rock trajectory of their own. They saw the Angelfish video, met Manson in London and suggested she improvise over some rough cuts. It was more than awkward - apparently, she stormed "I can't sing this bloody crap" - but she returned with lyrics, black as pitch and twice as sticky, that pulled everything together. She flew with her considerable baggage to Wisconsin, where the rest of Garbage live, installed herself in a hotel and became a partner. "I'd never written a word or a note before. Desperation was my impetus. I said, sure I can do that, and wept down the phone to Scotland every night."
But not for long. Writing became easier, and then became redemptive. "It's metamorphosis, alchemy - you take something dark and it comes out beautiful. Before, I had no expression at all, no voice. But when you write, you expel the waste from your body. An analogy I like that's particular to women is when you're bursting on a pee and it feels like you're close to orgasm. Do you know that feeling?"
No, but don't stop, let's charge right into Pseud's Corner. Luckily, she's laughing. "When your bladder's so full it's pressing on your uterus, I imagine, then when you try there's a second when you can't go, you're so bottled up, and then," Meg Ryan-beating gasp ... "there's that huge release." Briskly: "One of the greatest feelings in the world, I'd say."
The facilitators of all this, like avuncular therapists, cannot be praised enough. "Butch, Duke and Steve have allowed me to tap something that was previously squashed inside, eating me alive, and they've never said a cruel word to me, never once made me feel small or embarrassed or diminished. We're a marriage, and I see my meeting with them in biblical terms."
You wonder where this leaves Eddie, the sculptor she married two years ago. Fortunately, he is happy in his studio and does not mind the separations. For this and other reasons, he sounds like a saint. "I'm riddled with neuroses, I'm the female Woody Allen, but Eddie totally embraces my compulsive and impulsive sides - I think he thinks it's funny." Keen to have children, she worries about "wreaking havoc on their psyches"; it'll be some time before she can do either. The couple bought a house last year, and she has seen it twice. "Everything I cherish is over there. We have a beautiful clifftop garden, along the coast from Leith ... But this is my honeymoon period in the band. And I'm determined to enjoy it, because it can't exist for ever."
Butch Vig too, is making the most of his window of opportunity. I speak to him, briefly, backstage before the show at Atlanta's Tabernacle, a customised Baptist church with unlockable saloon doors on the toilets. His nails are covered in chipped maroon varnish, but you can hardly see them since, to keep his wrists supple, he thunders his drumsticks on the table throughout our conversation. Apart from the drumming, he is a quiet man with a star-studded cv - among other things, he produced Nirvana's breakthrough "Nevermind". Garbage was Vig's idea, though he is seldom asked about it, and seems happy to reside in Manson's shadow. Like Erikson and Marker, he had always wanted to be on the other side of a mixing desk; when they met at college, in 1978, being a band was their original plan. "But people just wanted to hear covers. We'd throw in one of our own songs, and after 10 minutes they'd yell 'That ain't by Lynyrd Skynyrd', and beat us up. Ah, we suffered for many years."
Born in Wisconsin's Fargo-esque badlands, where his family would trill Norwegian folk songs around the piano, Vig became a cab driver after college, then a short-order cook. Humility set in early. "I had to get up at 4.30 and ride my bike to this place. My boss was 60 years old and an asshole. But worse, it was at a girls' dorm. This one girl - Greek, gorgeous, dating a quarterback - wouldn't give me the time of day. Eventually I quit the job: I got drunk, called my boss, and said 'I just can't stand you, man'. A year later, the girl came to one of our gigs. I went over and said, 'How's it goin?' She didn't even know who I was." He shrugs. "It's done. I don't even care now." There is a deafening hurricane of drumming.
The experience with one difficult woman has not soured him. "Shirley was actually a little more tactful than she says when she first met us. Not now, of course, she doesn't hold anything back."
Manson, he explains, was less a slap in the face at the start, more of a catalyst. "She threw a monkey wrench into the works, twisted everything up, but I can't imagine the sound at all if we'd worked with anyone else. There's a chemistry between us; without her, I wouldn't be talking to you now."
And the future? He looks down, drumming on his knees. "We'd love to score a film. Uh, we've been approached by David Lynch, and Ron Howard. Nothing concrete, y'know. We're just pop geeks." Hardly.
There's a tap on the door, a bit of bustle amid the cocktails and Miles Davis CDs with which this patently suave band ease themselves into the night. Watching them, moments later, entertain 3,000 Atlantans with their dark glamour, you realise that all four have at last found their place. There's a single ready for release, called "When I Grow Up", and Shirley sings it just like Debbie Harry. It's about "that delirious state of wishing and hoping and dreaming for things, not giving up", she told me earlier in the day. "There's a great quote by Flaubert where he says, 'Sometimes the forces of the world hold us back for a while, but not for ever' ... "
Actually, it occurs to me, this band's story could run and run.
Garbage tour the UK in January: Belfast King's Hall, 15; Birmingham NEC, 17; London Wembley Arena, 20; Manchester Evening News Arena, 22; Glasgow SECC, 23.