If Your Opponent Taps Their Lands In Response Drain Power, Do You Still Get The Mana Provided Your Opponent Couldn’t Spend It All?

Basically You

Cast Drain Power

Your opponent taps 5 lands in response. They have 5 mana floating

They spend 3 on an instant/ability. They have 2 left, but have no way to spend it.

Do you get 2 mana since it was in their mana pool while Drain Power empties it? Or none since none of it wasn’t through Drain Power’s land tapping effect?

Basically You

Cast Drain Power

Your opponent taps 5 lands in response. They have 5 mana floating

They spend 3 on an instant/ability. They have 2 left, but have no way to spend it.

Do you get 2 mana since it was in their mana pool while Drain Power empties it? Or none since none of it wasn’t through Drain Power’s land tapping effect?