Two different things.
Overflow or recovery tank just catches what comes out of the radiator when the cap purges pressure and hopefully puts it back when the coolant returns to normal temperature. An overflow tank is not sealed, it is open to the atmosphere.
A pressurized tank link in all late models, also know as a surge tank, degas bottle, or expansion tank is different in that it is part of the sealed system. The fill line in the degas bottle must be higher than the radiator or it will not work properly.
A degas bottle can be used in conjunction with an overflow tank but most OEMs have engineered enough air space into their tanks that it will never push fluid out of the cap.
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Donny
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