There seems to be no end to the argument over second fermentation in tanks. The French claim that Monsieur Charmat invented it, while the Italians admit that though the French may have put this process into practice it was actually invented by the Italian Martinotti.
That does not change the procedure: a large stainless steel wine container with fairly thick walls equipped with refrigeration systems and capable of resisting pressures of 10 atmospheres is used. The wine is put into it and undergoes a second fermentation under pressure.
Bottling is done using a counter pressure filler, which allows the wine to maintain the same pressure in the bottle that it had in the tank. This is how the bubbles in many Charmat/Martinotti method sparkling wines are achieved, but also those in many white wines and lively, semi-sparkling rosés.