Volvo D1-20 Oil removal

[DeeJayPee]

I used to pump oil out of the dip stick tube.
However I now notice a pipe coming from the bottom of the sump which has a black cap on it. 
Does anyone know if this is a sump emptying pipe, and if so how does the black cap come off?

[IslandAlchemy]

That is the emptying tube.

[Moodymike]

The black cap just pulls off.