Plumbers?

yes, you need a vent. 3" minimum for a toilet...
Plumbers claim that you can plumb a bathroom no matter where you put it. But the farther you locate the bathroom from your home’s main waste line, the more problems you’ll encounter. The main waste line is a 3- or 4-in. dia. pipe called a “soil stack” when it runs vertically inside the house, and a “building drain” when it runs horizontally underground. On the main floor, it’ll be enclosed inside finished walls, but you can usually locate it by looking in the attic or basement or on top of the roof, where it exits to open air. You’ll have to attach at minimum a 3-in. dia. waste line from your new toilet to this main waste line. The shorter the run, the better, so you don’t have to break into as many walls, floors and ceilings. In extreme cases, you may have to box in a portion of a ceiling for a drainpipe.