If a large shareholder wanted to sell their entire stake (Take Elon for example) How would they do it to avoid slippage/market impact?

Let's say Elon Musk wanted to sell his 13.4% stake in tesla (according to google). Here are my questions:

1) How would he sell it to avoid affecting the price. I would assume selling on the open market would be a terrible idea.

2) How long would it take to sell a stake of this size? (Assuming the shareholder want to liquidate his stake ASAP without huge market impact)