This big boi is definitely bigger than the Unlimited Blankness. The small portion of the water bottle that is air contains all spaces; yes, including The Unlimited Blankness. The water portion of the water bottle is made to represent the biggest verses with actual stuff in it.
The cap of the water bottle represents a cage that keeps all reality inside, otherwise reality will fall out, causing possibly the biggest extinction event since The Thirsty One drank an entire water gallon instead of water bottle like usual, which destroys tons of verses just by him drinking. This cap is also an (futile) attempt to stop The Thirsty One from drinking the water out of the water bottle.