Answer:
Round like a dishpan and smaller than a bathtub. But the ocean can't fill it. What is it?
What goes in the water red, and comes out black?
A type of hammer that brings a room to order.
In we go, out we go. All around and in a row. Always, always steady flow. When we'll stop, you'll never known. In we go, out we go.
The root tops the trunk on this backward thing, that grows in the winter and dies in the spring.
Almost everyone needs it, asks for it, gives it. But almost nobody takes it.