What the other guys are talking about is oil that seeps out of the main bearings, pools in the hot-section, then smokes on initial light-up.

What you are talking about is a vent tube on the bottom of the cowling, correct?

The T-45 does this, as does the T-1A / Beechjet, and I think the Airbus.

I'm pretty sure it is an oil vapor vent from the oil tank.