A small pipe is used to carry water, usually from [[Large Pipe]]s to objects needing water ([[toilet]]s, [[sink]]s, etc.).
However, the water does dissipate after 40 tiles. Prisoners cannot escape through small pipes, as opposed to large pipes.
Pipes can not be built through a [[Perimeter Wall]] (or [[Water]]), and building a Perimeter Wall over any existing pipe will remove it. It is not possible to build a small pipe over a large pipe. The large one has to be dismantled first.