Just go into some woods or something. But if you have to smoke in the garage, do one of the following (or both);

Grab a pillow, and take it into the garage with you. Whenever you need to exhale a hit, blow it into the pillow. It'll obsorb most of the smell and prevent it from filling the room.

and/or, do as stated by sirkills, and spill a little bit of gas. But you should really try to blow the smoke out a window.