What is this bolt? A drain or plug of some kind? Pic included.

Wrapping up a head gasket replacement on my Prius V. When reconnecting the oil pressure switch and crank position sensor on the back side of the engine, just above the oil filter housing, I noticed this drain plug or something. I don't know what this bolt is for. It seems like some sort of drain plug.

This pic is not mine, by the way. My bolt/plug was much filthier with oil. I assume this may be an oil leak point. I will remove, clean and reinstall with threadlock.

But, does anyone know what this bolt or plug is?

 

Thanks, @Mendel Leisk. According to the Gen 3 manual you link in your signature, this bolt is called the Taper Screw Plug. I called my local dealer and they have this part listed as the Oil Pump Plug (a drain plug for the oil pump).