Turbo wastegate!!!
If you follow it, it will go thru a solenoid valve (bolted under the battery) then on to the turbo actuator. If you have a bleed valve then this will be in the pipe line (Is the hexagonal silver thing next to the overflow coolant pipe the bleed valve - looks like it, as its not standard!!!)
The thicker one is your brake servo and the transparent one underneath will be your boost guage - this as std would have a rubber nipple to blank it off.