This plumbing vent stack is made from 2" ABS pipe that protrudes up through the roof. A plastic and rubber flashing goes over top the vent pipe. The rubber top on the flashing is supposed to be self-sealing around the pipe, but because of the steep angle of the roof, the rubber didn't fit tightly around the vent pipe. I put some silicone around the joint, then put a second rubber flashing over the vent... similar to the storm collar that goes around the chimney.
The vent flashing is also just like the chimney flashing in that the shingles sit on top of the flashing on the upside of the slope, and the flashing sits on top of the shingles on the downside of the slope.
On underside of the roof, the pipe is secured to the roof framing with pipe strapping. The bottom end of the vent stack will eventually connect to the rest of the DWV (drain/waste/vent) system.