It's tempered glass and very thick. Very very sturdy.
It can either be plumbed into the intake or vent directly to atmosphere.
I know lots of people have done this in the past, myself included, but wasn't this determined to be incorrect? The engine must be under vacuum at all times. Out of boost, the manifold pulls through the PCV to maintain negative pressure. Under boost, the manifold has positive pressure, so the vacuum must come from somewhere else. That somewhere else is the port on the driver's side valve cover, which is connected to the stock airbox or aftermarket intake nipple. When under boost, the turbo is sucking enough air to lower the pressure in the airbox or intake tubing, thus pulling through this port on the valve cover.
Many threads over the years have mentioned issues with oil control, seals, and even loss of power when eliminating this source of vacuum under boost. A catch can and/or check valve in the path is fine, but this nipple should be connected to the one on your aftermarket intake. After all, there's a reason they put it there.
Edit: ah, looks like you found some posts as well