As Bob said, visit your local hardware or plumbing supply store. Take some of the parts you want to connect as the Fluval is a German product and as such, as Agro said, will be metric. IF your like me, the only metric conversion I really know in my head is ~2.5 cm = 1 inch.
I modified a HOT Magnum years ago with PVC I had lying around - works like a charm to this day.