Playing with offline youtube videos, a question.

You can have the youtube app download your subscriptions, videos you tagged to watch later, or if thinks you might like a video based on your history while on wifi so you can watch them later without eating your data.

Where are they stored so I can go in later and delete them to clear up storage space? If I delete a video from my watch later list, is it's cached data cleared up on my phone's storage too? Can I only clear them all by clearing my youtube's cache, not picking and choosing what to keep?

I just have it set to save my 'to watch later' videos offline, but I'm not sure deleted them off that list is really deleting them off my phone.