Tanks are 2 by 2 sealed rooms that are randomly generated in the Dungeons of Doom and are not connected to other rooms/pathways (similar to a vault). They contain pools of water and 2-6 pieces of worthless glass in all four squares, and 1d4 - 1 aquatic animals. The Big Room and the Rogue level never contain any tanks.
On any level that does NOT contain a vault, there is a 1/6 chance of a tank being generated.
Finding and getting into tanks
The following messages tell you there is an aquarium on the current level:
- You hear the bubbling of an oxygen filter.
- You hear frenzied splashing. (Tank contains at least one aquatic monster)
- You hear gently lapping water. (No aquatic monsters, but at least one square still has a pool of water)
There is 67% chance it can be accessed through a closet that contains a teleporter, recognized by the engraving "ad aquarium" (Latin for to the water room) in front of it. Unlike a vault with its stock of gold, there is generally no reason to seek out a tank, and indeed they are more likely to be deadly (unless you can walk on water, are flying or levitating, or have magical breathing - although in the latter case, items in your inventory are at risk of water damage, and in any scenario, you will still need to deal with the creatures in the tank). If you can handle the pools and their inhabitants, then it can sometimes be helpful to #name-identify the worthless glass.
Due to the similarity of the engraving for vault teleporters an tank teleporters - especially once those engravings begin to degrade - the unwary explorer might mistake one for the other. Woe betide the adventurer who jumps into that teleporter looking for gold, only to drown in a fish tank.