In the early '80s, Einstürzende Neubauten wrong-footed their audience by doing away with drums, instead drilling and hammering on scrap found in the ruins of West Berlin. 35 years later and a few hundred meters beyond the former Berlin Wall, two men are stood on a stage doing something similar. Only it's not scrap metal they're performing with but a washing machine with the cuddly name Ultimate Care II, still-functional and partway through a cold wash. They're not thrashing it but gently prodding and caressing it, sometimes reaching carefully inside it as if midwifing an animal. And they're not topless and sweaty but calm and well-dressed. One of them is wearing a tie.

A third performer, sat at a low table in front of the stage, teases clusters of washing machine-derived samples out of a pair of Apple laptops. The sounds zip and ping between two giant Funktion One stacks, gradually forming into a beat. The drummers respond accordingly, paradiddling on the machine's fittings, tap-tapping its clunky settings nobs and rubbing their wet fingers down its dinted sides to make comical shrieking noises. After 40 minutes, the wash cycle finishes and the performers stop. The crowd applauds enthusiastically and the musicians leave the stage. The washing machine stays where it is, 130 pounds of inscrutable metal. I wonder if it's the only washing machine to have seen the inside of Berghain.

The Ultimate Care II is slightly younger than me, having been made in about 1991. The model is no longer produced, and this one had already led a long life when Drew Daniel and Martin Schmidt moved to Baltimore from San Francisco six years ago. They bought a house, and the Ultimate Care II came with it. Daniel spent his days at Johns Hopkins university, where he was an associate professor in Renaissance literature. Schmidt, the househusband, spent hours with the machine, obsessing over "getting whites whiter," as he said in one interview.

Absorbed in the machine's rhythmic droning, a thought struck him. It was his turn to come up with an idea for the duo's next record as Matmos. What about an album using only sounds made by the Ultimate Care II? They conducted some experiments and instantly knew they were onto a winner.

"As soon as I started looping and collaging and assembling we just had a feeling like, 'Oh, this is going to work,'" says Daniel. It's the day of their Berghain performance and we're sheltering from the rain in the lobby of the pair's hotel. Daniel is the guy with the two laptops; he's got one of them handy now, and slips it out of its case to play me some recordings of a metal shelf he and Schmidt found in their hotel room that morning.

Schmidt is one of the washing machine whisperers—the other, Adam Rosenblatt, a young percussionist enlisted for the tour, is absorbed in his screen a couple of meters away. Schmidt plays the shelf in the same way he will later massage the Ultimate Care II. Daniel skips through the audio file, keeping his laptop speakers low to avoid bothering the other hotel guests.

I'm between Daniel and Schmidt in a row of low armchairs. They were sitting together but parted for me when I arrived, and while we chat they trade affectionate banter across my lap like tennis pros mid-rally. They're dressed in their usual uniforms, which seem designed to make their half-decade age gap appear larger. Daniel, in a Return To Forever tee and frayed denim jacket, periodically fiddles with his shoulder length hair. Schmidt hasn't yet donned the tie, but a suit jacket and trousers in muddy browns shore up the geography teacher look.

They've just arrived in Europe for a nine date tour in support of Ultimate Care II—the 40-minute album built around the machine. The Ultimate Care II—the machine itself—was despatched from Baltimore a month ago and collected from German customs this morning. It's waiting for them at Berghain. They can't relax just yet, though. "I haven't actually clapped my eyes on it," frets Schmidt. "It could have fallen over and be in pieces for all I know."

"If it doesn't run properly we'll have to freestyle the show," says Daniel. "We'll play a suite of pieces, but we won't have the live component of the machine. Which would be a different show."

Even if it's in one piece, there are other unknowns. Will an old American washing machine run well on European power converters? Will sticking a couple of mics in an empty metal drum cause irresolvable feedback problems? What about Berlin's hard water? The show, which has been painstakingly timed to the length of a wash cycle, can easily get out of whack. "If we don't clean the filter before every rehearsal and every performance then lint impacts the intake and it can take a really long time to fill," Daniel explains. "And then our whole show is too long. You have to do this weird math in your head, like if each fill was eight minutes instead of six, then that means that the event that usually happens at 30 minutes now would take place at 34 minutes."

Then there's the part where they lug 100 gallons of water onstage in a large rubbish bin. (The machine has to get its water from somewhere.) "We've done a load-in where they're like, 'You're gonna do what!?' And we're like, 'It's OK, we brought a towel!' Somehow that doesn't calm them down much."

Schmidt pipes up. "There is one risk… The output hose where it gushes out has in fact become loose before, and water just goes bwhooaar." He swoops his arms out in a dramatic gushing movement. Daniel cuts in. "And when that happens there's nothing you can really do. You are fucked."

"You can't shut it off because it uses gravity to make the water come out," Schmidt says. "So the only option is to shove your thumb in it and then…" He pulls a comically desperate expression.

They seem pretty relaxed about the many ways in which tonight's show could go horribly wrong. Then again, they're veterans of this sort of thing. Daniel and Schmidt started their musical and romantic relationship in 1995, and soon joined a vanguard of musicians exploring the possibilities of sampling and digital music-making. Their studio exploits are well-documented, from 2001's A Chance To Cut Is A Chance To Cure, which sampled the sounds of plastic surgery, to 2013's The Marriage Of True Minds, a sprawling album derived from parapsychological experiments. Perhaps less recognised are their equally ambitious live shows.

"It's just a question people ask when you tell them, 'I make music,'" says Schmidt of the project's early days. "They go, 'Oh, when are you going to play live?' And we were just sort of like, 'Oh, right.'"

"So we brought our tower computer and a lamp," continues Daniel. "It was like moving in, because there weren't laptops. This was, what, '95? It was a long-ass time ago. Our first shows were in ambient rooms at raves. Pretty early on we would bring a banjo and Martin would improvise and I would sample him live. It was about manifesting the process from object, to pattern, to the field of options that samplers and software give you."

Since then they've found numerous solutions to the problem of making a laptop-based show—where the link between gesture and sound is broken—engaging. They've played with 25 drummers at once and with an Enigma machine; they've worked with a "volunteer choir" of audience members and had ten people play a metal railing using roses as drumsticks. That's not to mention the year they spent on the road with Björk, adapting her Vespertine LP for the stage. "Matmos is supposed to be a very polymorphous perverse kind of amoeba that can have a lot of different shapes," says Daniel.

Is shipping their own washing machine to Europe their stupidest idea yet? "It's hard to say." Daniel thinks. "We've definitely done some foolhardy things in the past. Probably playing a cow uterus live was more…"

Schmidt: "More personally disgusting, certainly."

Daniel: "And more conceptually flawed."

"And failure-ridden. Because they come from a farm-supply catalogue. We assumed that they're for practicing artificial insemination, and if you're practicing that, it doesn't matter whether the uterus is intact."

"It doesn't have to be airtight," continues Daniel. "But for musical purposes it really makes a difference."

"Yeah, because basically what we are doing is making a shitty bagpipe out of—"

"—out of a vagina—"

"—and time and time again we would open the plastic bag, which is filled with this noxious formaldehyde. And they're crudely stitched shut, and you're just like, 'It's not gonna work!'"

"I can't possibly work under these conditions," Daniel huffs, playing the prima donna.

So why do these things at all? Surely there's an easier way?

"We want to avoid that kind of flawless, airless, trade-show vibe of, 'Here's my content and it's immaculate—'"

"—though in fact," Schmidt interrupts, "that is what people want. We played Sónar a few years ago and the sweet people at Sónar put us on a bill with—"

"—Jon Hopkins—"

"—and I guess he's actually playing live. It doesn't matter, because his thing is so flawless that it might as well be a tape. Like, it starts before the guy even walks on stage, he comes out, looks down at his equipment, and huge perfect music comes out. And everyone loves it. Sure enough, we came out and did our weird thing, and people were like, 'Ooh yay, I guess…?' I'm not trying to diss him, I just—"

"—it's just, for us, it wouldn't be worth doing."

I wonder if they'll be saying that with the same confidence when soundcheck gets underway. I catch up with them at the club a few hours later. Outside, the weather has run a full cycle, the morning's drizzle giving way to heavy rain before draining away to leave clean blue skies. The band's soundman is caught in traffic, but Daniel was anxious to come early and look things over. The washing machine is there, and it's in one piece.

Rosenblatt, the percussionist, taps it experimentally. Schmidt explains that he has only rehearsed on the replacement machine they bought while the Ultimate Care II was in transit: an original model Ultimate Care. "Which sounds a little better!" he whispers conspiratorially. Daniel calls across the room. "Did you get a bit sweet on the Ultimate Care? You're going to hurt its feelings."

Schmidt and Rosenblatt lift the machine onto the stage and start piping it up. The Berghain crew blow the cobwebs out of the speakers with some Tame Impala and the lighting rig runs busy test sequences. Crates are wheeled behind the bar and a pug wanders disinterestedly across the dance floor. Daniel roams the club, stretching and cracking jokes. Schmidt asks one of the crew to find him some "old man cigarettes."

The soundman arrives, but there are teething problems. One of Daniel's audio interfaces is broken, and, as predicted, the microphones pointed at the Ultimate Care II "feed back like a motherfucker." Schmidt shouts instructions to the soundman. "Did you roll off that 100-and-whatever frequency? Somehow you need to goose the monkey quality of it. Goose the monkey!" He rubs his finger against the metal, producing a primate shriek.

"If we're gonna start the machine we should do it pretty soon," says Daniel. A soundcheck takes 40 minutes—there's no way of skipping through the wash cycle—and show time is approaching. Schmidt twists an ungainly knob and the machine starts sucking in water. He turns to his digital synth, set up at the side of the stage, and he and Daniel play a few minutes of tense, atonal improv.

Something's not right. "We're at seven minutes, still filling," shouts Daniel from behind his laptop screens. After eight and a half minutes the machine finally enters its next phase—an ominous rhythmic chunter—but it sounds weird. "It's kinda slow," Rosenblatt says, peering into the machine. Then he realises that the pump that drawers water out of the rubbish bin isn't running. Then the power cuts out.

The crew swarm over the stage, clucking and arm-folding. It seems that the pump and the machine together draw too much power from the voltage converter. They put them on separate circuits and the Ultimate Care II springs back into life with a sinister thunk. The band try to pick up where they left off but the machine stops again. Daniel has lost his composure. "Fuck, fuck," he mutters, skimming a PDF of the Ultimate Care II manual he just found online. They get the machine going again and everyone's lost their place in the cycle. "Now we're in drain, we're not in chug?" Daniel shouts. "Shall I continue to play?"

I slip out for some food, returning as the club doors open. Daniel is lurking tensely by the merch stand, where they're selling bars of Ultimate Care II soap. I ask if everything's OK. "Everything's not OK," he replies. "It's fucked." The machine and the pump are still drawing too much power. They've sent somebody out to buy heftier converters, and Daniel has a "contingency" if that doesn't work out.

Upstairs, the support act, Klara Lewis, is performing from the sound desk at the other side of the room, meaning we're all left staring at the Ultimate Care II. Her blurry video projections play across its surface. An hour or so later, Daniel, Schmidt and Rosenblatt stride gamely onstage and make a classic Matmos start: Daniel attempts some banter in German (he did the same thing in Spanish when I saw them at Sónar), and Schmidt tells a few goofy jokes.

They start the machine and Daniel and Schmidt begin their improv section. It seems that the new converters did the trick: at the predicted time, the Ultimate Care II chugs into its next phase and the show goes on. Rosenblatt and Schmidt drum busily, sometimes sliding out of time with one another, or sticking their mics into the machine to capture the rhythmic sloshing sounds. At one point Rosenblatt uses the fabric conditioner dispenser as a guiro. The music alternates between twitchy beats and spooky arrhythmic sections, while a video projection shows us tumbling ever deeper into the innards of the machine, Through The Looking-Glass style.

The set isn't identical to the album, but it ends in the same way, with a hyperactive gabber workout. As the wash cycle ends, and before Daniel leaps up on stage so that the three of them can take a ragged bow, Schmidt and Rosenblatt finish with one last hearty thwack on the Ultimate Care II's frame. Maybe I'm imagining it, but there seems to be a lot of relief in the gesture.

Earlier, Daniel had insisted that Matmos isn't a "persona-driven" project, but I'm not so sure. Matmos's shows, like their conversations, are funny and intelligent and full of unexpected detours. It's their personalities that have sustained this bizarre project over two decades, and it's those personalities that are on stage when they perform. Surely there's no better way of acknowledging this than to bring a 130-pound chunk of your domestic life on tour with you.

"We've always been a band and a couple, we've always been both," Daniel says. "We don't have a sense of, 'Now we're Matmos, now we're not Matmos.' We're Matmos when we're brushing our teeth. People talk about life-work balance and I don't think I know what that is. It seems all one."