Did Snape really give Umbridge a fake Veritaserum potion that Harry later pretended to drink?

Question

The Harry Potter Compendium page for Veritaserum states the following:

Dolores Umbridge attempted to use Veritaserum on Harry the following year, but to no effect. In actuality, Snape had presented her with a fake potion, and Harry only pretended to drink it, instead dumping it in one of her plants while she was occupied

However, I tried to find the relevant passages in Order Of the Phoenix that mention when Harry dumped it, and when it was proven Snape had given a fake potion, but couldn't find it.

Is that really in the books?

Answer 1

From Chapter 28, 'Snape's Worst Memory':

BOOM!
The very floor of the office shook. Umbridge slipped sideways, clutching her desk for support, and looking shocked.
'What was — ?'
She was gazing towards the door. Harry took the opportunity to empty his almost-full cup of tea into the nearest vase of dried flowers. He could hear people running and screaming several floors below.

(The "BOOM!", for the record, was Fred and George setting off fireworks.) As for the fake bit - to begin with, it seems quite likely as Snape was a spy and also hated Umbridge just as much as anybody. Further, in Chapter 37, it says

“Harry, you know that Professor Snape had no choice but to pretend not to take you seriously in front of Dolores Umbridge,” said Dumbledore steadily, “but as I have explained, he informed the Order as soon as possible about what you had said. It was he who deduced where you had gone when you did not return from the forest. It was he too who gave Professor Umbridge fake Veritaserum when she was attempting to force you to tell of Sirius’s whereabouts...”

Another relevant passage is from Chapter 32, 'Out of the Fire':

'Ah, Professor Snape,' said Umbridge, smiling widely and standing up again. 'Yes, I would like another bottle of Veritaserum, as quick as you can, please.'
'You took my last bottle to interrogate Potter,' he said, surveying her coolly through his greasy curtains of black hair. 'Surely you did not use it all? I told you that three drops would be sufficient.'
Umbridge flushed. 'You can make some more, can't you?' she said, her voice becoming more sweetly girlish as it always did when she was furious.
'Certainly,' said Snape, his lip curling. 'It takes a full moon-cycle to mature, so I should have it ready for you in around a month.'

Answer 2

The passage mentioning Harry dumping it is in Chapter Twenty-Eight of Order of the Phoenix:

She was gazing toward the door; Harry took the opportunity to empty his almost full cup of tea into the nearest vase of dried flowers. He could hear people running and screaming several floors below.

The passage mentioning that Snape had given Umbridge a fake is in Chapter Thirty-Seven:

“Harry, you know that Professor Snape had no choice but to pretend not to take you seriously in front of Dolores Umbridge,” said Dumbledore steadily, “but as I have explained, he informed the Order as soon as possible about what you had said. It was he who deduced where you had gone when you did not return from the forest. It was he too who gave Professor Umbridge fake Veritaserum when she was attempting to force you to tell of Sirius’s whereabouts...”