The oilreturn under the turbo, altough people say just a screw-on jobbie isn't enough. And you should have pipe on it wich go's down into the sump under the oil level to prevent oil getting trapped in the separator.
The bigger outlet on the separator is the vent. For that fit a big hose long enough down along the chassis rail to the bottom of the car. ( i presume your talking the bailey style oil separator? )

succes, Rinus