Hello

I just got my Empty Green Brewfest Stein, and I accidentally filled it from the wrong keg. :(
It is now a Filled Green Brewfest Stein, and I cannot figure out how to make it empty again.

I cannot fill it from a different barrel because it tells me I need an empty stein. D:

Is there any way to empty this thing out? I have tried drinking from it multiple times and it stays filled!

THank