Dry wall in the bathroom is bowed or pushed out by the vent
pipe inside the wall. There is no way to adjust the position of
the vent pipe. I need to straighten the dry wall to install tile on
the wall. Would adding firring strips to the studs that are set
back help to create a level wall?
Yes, adding furring strips (on,, not across, the studs) will let you make the overall wall more flat. Although I have not seen example, I have the impression that bowing of the wall surface would be more noticeabvle with tiles as opposed to just a painted wall.
You may need furring strips of varying thicknesses depending on the nature of the bowing. For a vertical pipe that sticks out, most likely each strip itself would be of a uniform thickness but if the studs themselves are cureved you may need to use myriads of paired wedges on the studs to achieve a flat wall.
It is difficult to shop locally when the locality slaps you with a fine if you are a little slow getting back to your car.