Oil Drain requirements: A gravity pitch to the pan and as little restriction as possible is necessary. A scavenge pump can be used to return the oil if a gravity pitch is not possible on your application. Avoid 90 and 45 degree fittings as they can restrict return flow. The return should be above the oil level in the pan and away from crankshaft windage whenever possible, preferably in front of a main web, otherwise high and forward of the oil sump in the pan, (applications do vary and it is your responsibility to make sure the line is installed correctly and in the proper place.)
The oil return line should be as large as possible. A minimum of a -10 AN line is recommended with small and mid-frame turbochargers. A minimum of a -12 AN line is recommended with large frame turbochargers.