Fire fighting

Today we have visited a fire engine museum. There were not only old fire trucks but also fire fighting methods before the engines. Horse-drawn fire trucks and the most common thing of fire extinguishing .... the water bucket. Now I wonder if anyone knows or dare to guess why the bottom is cone shaped? (As the one to the left) I did not know, but know now.

The answer:
A bucket with plain bottom floats on the water. (When you through the bucket in the well or lake or so. You have to tilt it to let the water in). A cone shaped cut through the water surface and sinks. And is filled with water. Thus it is self-fulfilling. Cool or not?