The hilarious actress swapped iced water for milk - and jokingly declared it was actually her breast milk at that.
In the clip, she says she "couldn't find any water" and that the bucket of breast milk had taken her "all night to make."
She was nominated by Glee star Dianna Agron and child actor Ty Simpkins to take on the challenge.
But she actually had to take to Twitter to confirm that the milk was not, of course, from her breasts. C'mon people.
Oh wait some of you thought that was really breast milk? Oh dear. Uh thank you? But my boobs aren't that generous. Haha.
- olivia wilde (@oliviawilde) August 24, 2014
Olivia gave birth to little Otis back in April, and recently appeared in a Glamour magazine shoot looking beautiful as she breastfed him.
In the mag, she said: "Breastfeeding is the most natural thing. I don't know, now it feels like Otis should always be on my breast. It felt like we were capturing that multifaceted woman we've been discussing - that we know we can be. You can be someone who is at once maternal and professional and sexy and self-possessed. [But] I mean, I certainly don't really look like that when I'm [typically] breastfeeding. And there's usually a diaper involved."