I found this on Tsukune's "powers" page.
Yoki Drain: He can drain Yoki energy (spirit energy) from yoki and anything with spirit energy including demons.
Unlike the other powers on this page there is no stated example of this happening and I couldn't find one anywhere. It think it may just be misinformation. The closest I could think of is when Tsukune was on the verge of dying from not being able to control his Yoki with his human body, Akua Shuzen created a spell circle which would allow herself, Kokoa, Ruby, Mizore, Kuruma, San, Gin and Haijin to transfer some of their energy into him, though this could only have been done with the spell circle.
But if there is an example in the manga or the anime, please tell me or put that back on the page. thank you.