On all Gulfstreams, G2 through 550 the outflow valve is in the front, and all smells from nice to nasty pass through the cabin from the rear galley and toilet, on the way out.
The DU fans pull the air into cockpit.....fart in the galley and within 30 seconds there are screams of disaproval from the flight deck.......ask me how I know this.
Tony
I hope the galley and toilet in the pictures above look better in real life!!