Engine bay is a good place to start!!! lol, that big round thing sitting near the top of the engine closest to the window, unscrew the bolts holding it in and itll come off completly, therell be pipe attached to it which you might need to remove. G
Get a mate to sit in the car and rev it, youll see a ickle flap opening and closing, make sure your mate revs it enough to open the flap, spray the boost in there!!!
If its owt like mine, a load of smelly sh*t will come out