ON THIS WIKI
|Affected by Gravity||No|
The Raintank is a machine which collects water from rain and rainstorms. It has an internal tank capable of holding 30 buckets of water. Despite this, the tank still can't hold all the water from an average rainstorm.
So when it starts to rain, the tank gives off a redstone signal to start engines pumping automatically. (This is disabled in SMP)