Open Metal Barrel
Open to the Sky
A single-block fluid tank open on top, holding 12,000 mB. Fluid can be poured in by hand, and it slowly fills with rainwater when exposed to open sky.

The top is fixed as input-only; the bottom can be cycled between input, output, and off with a Hammer. Only accepts liquids, not gasses. Fills with rainwater when it's raining directly above and the tank is empty or already holds water — faster during a thunderstorm. In hot biomes it evaporates instead. A comparator against it outputs a signal proportional to how full it is.
