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.