Tubes, garden hoses, highways with water, sewage pipes, water pipes, canals, rivers of cells, Erie Canal, the Panama Canal, the Suez Canal, this canal, a stream, a brook, a storm drain. In short they are kinda like any kind of circular liquid transport system.
METAMIA is a free database of analogy and metaphor. Anyone can contribute or search. The subject matter can be anything. Science is popular, but poetry is encouraged. The goal is to integrate our fluid muses with the stark literalism of a relational database. Metamia is like a girdle for your muses, a cognitive girdle.