How did you do it so that the tax authorities and the bank manager would not question where the money came from?
I don't really know how this applies to all countries, but from my experience of changing Bitcoin and other crypto coins, the tax has been set on the exchange at a percentage.
Let's assume we change 1 BTC for $70k. $70k if exchanged into fiat currency is a large amount that will make the bank suspicious. This can be done in stages [3 to 4 times].
Taxes, we cannot avoid them because all exchanges are under the regulation of legally registered government-owned entities.
I have never made a large withdrawal by exchanging 1 BTC to fiat but what I know is that Indodax sets a daily withdrawal if I'm not mistaken 250,000,000 IDR if you want to make a higher withdrawal then you can increase the limit again.
But I also don't know for all countries how the government enforces it, but for our country there will be no question because exchanging BTC to fiat is very common in the sense that many people do it without the need for banks to ask where this is from because the government has supervised and legalized it as a commodity asset.