The band's bassist made the comments while speaking at Seattle's Experience Music Project at the opening of new exhibition Nirvana: Taking Punk to the Masses, The Guardian reports.
Novoselic said: "Here was a man who would never clean his kitchen or take out the garbage, or do those kind of chores. But Kurt Cobain was not a lazy person. We came to Seattle and we recorded a demo. Kurt Cobain earned the money for that.
"He was a janitor and he worked nights. Basically he cleaned toilets - that's how he paid for that demo. That's how hard he worked. He was a compelled artist, who excelled at every form he wanted to do."
Novoselic recently reunited with producer Butch Vig and ex-Nirvana bandmates Dave Grohl and Pat Smear on Foo Fighters track 'I Should Have Known', from their current album Wasting Light.
Grohl later revealed that the musicians also played Nirvana hit 'Smells Like Teen Spirit' together in the studio.
> Ten Things About... Kurt Cobain
Watch Krist Novoselic talking about Kurt Cobain for the EMP|SFM Oral History Live! series in 2008 below: