Wikia

The Iron Waterproof Pipe from BuildCraft is a one-way pipe. It has up to five inputs and one output. It will send all incoming liquids in one direction. The direction can be changed by right-clicking the pipe with a BuildCraft Wrench. The output direction can also be changed by a Redstone signal. Every time it either loses or gains Redstone power, it will cycle to a different output. However, it will never output to a Wooden Waterproof Pipe. This combination of properties allows for players to accurately control its output direction from afar, via Redstone wiring.