Drain Pipe, Drains, Drainage, Plumbing Pipe, Plumbing Pipes, Drainage Pipes,Toilet Drain, Toilet DrainsAll drains must have vents and both vent size and location is guided by the State Plumbing Code. Shown here, a 4” PVC pipe, on the left, is stubbed up for the toilet drain. These pipes are roughed in approximately 12” from the back wall and need to have 18” on both sides either to the nearest wall or fixture. A 3” vent pipe, on the right, is stubbed up in the wall and will serve as a vent pipe. A 6” wall is required since a standard 2 x 4 stud wall would be too small for a 3” vent.