Oil drains on turbos can be the cause of many issues.Smoking, leaking oil and even turbo failure could all be caused by a poor or restricted oil return line.
 
Often the use of an -AN line is prefered as it is easier to install and less likely to fail.However most aftermarket flanges have a round drain hole  while the turbo has a square shaped drain.
 
These T3/T4 drains are machined from billet aluminium and employ an o-ring to replace the nasty paper gasket which is often poorly aligned to the turbo causing yet further restriction.
 
Both available is stock length and extended length to suite a variety of applications.
See images for dimensions.