Who drank the green potion when Voldemort went checking for the locket?

Question

When Voldemort placed his horcrux locket in the cave, he used Kreacher to drink the green potion before placing the locket in the goblet.

When Regulus found the cave, he drank the potion himself before Kreacher took the locket.

When Dumbledore and Harry went in the cave, Dumbledore drank the potion. So the potion drinking was essential to get the locket.

But when Voldemort found out Harry has taken the cup from Lestrange's vault he went to the cave alone to check whether locket was safe or not. Remember the potion wasn't transparent as Harry and Dumbledore didn't see the locket when they saw the goblet. They could only see the potion. And potion used to refill as it refilled after Regulus switched the lockets.

So, who drank the potion that time when Voldemort was checking for the safety of the locket?

Answer 1

No one

The potion was turned clear by Voldemort himself so he could look at the bottom.

As she said it, a wrath that was like physical pain blazed through Harry, setting his scar on fire, and for a second he looked down upon a basin whose potion had turned clear, and saw that no golden locket lay safe beneath the surface —
_{Harry Potter and the Deathly Hallows, Chapter 30, The Sacking of Severus Snape}

Voldemort was the one to create the potion and alone knew how it worked. With his experience in the Dark Arts, it would not be far-fetched to say he could make his own potion crystal clear.