Multi-Tank Extensions are a way to extend the size of your tank. Upon placement next to the core the capacity of the core will extend based upon the number of extensions connecting to the core. If you happen to place an extension that is not correctly touching another extension or core and later complete that connection the extension will update based upon a random peroid of time.
There are two methods of resizing a tank using extensions.
Place the various Multi-Tank Extensions next to other extensions or the core block itself. The core will resize based upon the number of extensions that are added.
Camouflaging the block is not just for ascetic purposes based upon the value of the material if you apply that block to the extensions(hold the hot key set in controls and right click the extension) the size of the tank will increased based upon value. Certain blocks such as cobblestone, grass and dirt are black listed and there for have a negative effect upon your tank, decreasing it's maximum size to 10,000 mB.
Various liquids can be piped into the extension or the core and therefore fill the tanks automatically.