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.

§lOperation§r
    - 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.