Anything but canon
(covers information that is anything but canon)
A whale tank made of material strong enough to withstand tons of water pressure
According to an account that was anything but canon, on the USS Enterprise, water pressure was handled by a man with an ass for a head, as well as a man with a screw for a head.
When the captain asked the two of them why they would have a desk on the bridge, they asked him if he actually thought that they had moved their console to the bridge. The only reason the captain asked them why they would be there is because he assumed that officers in charge of water pressure would be on one of the lower decks. Just as he said that, their console station started spewing water, indicating the pressure was too high. (VST: "Skin a Cat")