Exit your ship and walk off-screen to discover the headquarters of ScumSoft. When you get a chance, wear belt, and use belt to become invisible. You are ready to enter scumsoft. Walk into the building, and execute command "press the button" to find yourself inside. 
Walk up the hallway until you reach a door on the left side and enter it. That should be the janitorial closet. Pick up suit, exit the room, and walk down the hallway to the first door on your right. 
In the cubicle maze, you will need to pose a janitor (and do a good job doing so). If you check your pockets, you will find that your new outfit contains a new item: Mr. Garbage, which must be used on every wastebasket you walk by (use vaporizer). Follow path 1 on the next two images to get to the office of evil Pug.
Walk inside the office and use vaporizer on his waste basket. Walk to the balcony behind his office. When you return, Elmo will be gone. Help yourself to his office and take keycard from his desk. 
Retrace your steps back to the beginning (ignore the empty trashcans) and now follow the path 2 in the figure above. When you reach the picture of Elmo Pug, pick up picture and walk over to the copier to the left. Use machine to obtain a copy of the picture.  Walk back to the original location of the photo and replace picture to remain incognito.
Return to the hallway. Walk until you see a door with a keycard slot on the right. Stand next to it and insert keycard. Whenever you are notified that the machine is about to scan your face, use picture. 
Once inside, execute the command "press the button." Cross the bridge, and use vaporizer on the Two Guys From Andromeda.  After a quick arrest, you will be forced to battle Pug in a fight of Dukem Nukem Robots. See Appendix for more information on this mini-game.
After beating Pug, you will find yourself aboard the Aluminum Mallard.  Look at the screen and set yourself to Attack Speed, and go into the Weapons Systems menu . The strategy for this final fight is described in detail in Appendix. 
After defeating four of Pug's ships, they cease the pursuit, leaving you to enjoy the ending cinematic of Space Quest III.