drain

To drain is to empty, or to cause something to empty of liquid. (verb)

When you open the plug on a sink preventing water from going out and allow the water to go out, this is an example of a time when you drain a sink.
When a sink is filled with water has its plug opened and the water runs out, this is an example of a time when the sink drains.
When all of the sadness you were feeling leaves you, this is an example of a time when the sadness drains out of you.
When water runs off of a driveway, this is an example of a time when the driveway drains.
When soil becomes drier, this is an example of a time when the soil drains.
When you drink an entire glass of milk, this is an example of a time when you drain the glass.

A drain is a pipe or channel that lets something run off. (noun)

A pipe that lets water out of your sink and into the sewer system is an example of a drain.
A kid who takes all of his parent's money is an example of a drain on his parent's money.

See drain in Webster's New World College Dictionary