The small pipe is your oil return, but it depends on how your oil breather tan has been set up. One way is to return to the block on the turbo side, you would see an adaptor just up from the sump towards the back of the block, underneath turbo. Or, it could be set up to return direct to sump. (the preferred way) If it has been set up like this, you will likely see an adaptor on the inlet side, somewhere along the sump, very close to where the engine breather is located on that side i would have thought.