What is it with Silicon Valley billionaires and hot tubs? First we had Elon Musk admit in 2016 how he banned himself from discussing in hot tubs the probability of reality being a simulation. And now we have newly-resigned Uber boss Travis Kalanick, who is known to sit in hot tubs for up to 10 hours at a time.

The bizarre revelation first came out in 2015 when it was buried in the depths of a (now archived) Bloomberg article. But thanks to Dealbreaker the remarkable tale lives on.

The story goes that, back in the early days of Uber, co-founder Kalanick approached billionaire tech investor Chris Sacca for a cash injection from his fund, Lowercase Capital, which had previously helped kickstart Twitter.

Instead of throwing bags of money at hipsters with vague plans to change the world with a smartphone app, Sacca had developed a reputation for seeing how would-be recipients of his investment react in situations outside of business.

Bloomberg explains: "Sacca, an early investor in Twitter, has his own brand of due diligence in order to avoid bad deals...He invites entrepreneurs to his home in Truckee, California, near Lake Tahoe, and sees how they act over a series of home-cooked meals, hikes, ski trips and hot tubbing."

'I've never seen a human with that kind of staying power'

Sacca said he and his wife would "see people who wouldn't actually get up to put their dishes in the sink, and immediately be like 'No way. Like, there's no way we're getting in and doing business with them'."

No one knows how Kalanik coped with the cooking, hiking and skiing, but his 'tub sesh' skills are the stuff of legend. Sacca recalls: "Travis can spend eight to 10 hours in a hot tub. I've never seen a human with that kind of staying power in a hot tub."

Through Lowercase Capital, Sacca invested $300,000 (£235,000) into Uber's angel funding round and is believed to retain a 4% stake in the $70bn company. Despite this, it was recently reported that Sacca no longer speaks to Kalanick after the Uber co-founder became angry at Sacca for attempting to buy up more shares in the ride-sharing business.