We're having a Gaggenau Combi Steam oven installed and need to instal a drainage system for the hot waste water. Is there a PVC pipe that can be used or will we need to use copper?

How hot? You can possibly use CPVC but I would not use PVC.

Normally, you need to use black iron pipe for such an appliance. I know of no place that would allow any other type of pipe to be used. I have used silver soldered copper lines, but that is very expensive and few plumbers have the proper 5%-15% silver needed and oxy-acetylene torches. Black iron is the only kind of pipe you should use.