Here's James with the lye tank. The aluminum cans go in here.
His left hand is on the hydrogen vent hose. The gas that bubbles out of it is hot and steamy and has a fair amount of powdery white aluminum oxide in it. So next it goes into a pipe to the bottom of the white bubbler tank, where it bubbles through water. That makes it cool and clean.
Just like in a hookah or bong.