Drains are Nodes that consume Resources.
The rate of a Drain is determined by the flow rate of its input Resource Connection. Some Drains consume Resources at a steady rate, while others consume Resources at random rates or intervals.
You can also make a Drain consume everything its input Resource Connection is attached to by labelling the Resource connection with all.
In principle, you could represent a Drain as a Pool with no outputs, but to indicate that the Resources that flow are consumed and have no further impact on the game, it is better to use a Drain.