Someone can correct me if I'm wrong. The shops generally don't use inches and feet etc for PVC fittings. It's all mm. But if you are comfortable that unit system, then have a look on the fittings themselves, usually it says 3/4" etc.
As I see it you can use the 25mm PVC for the 1" outlet and for the 1.5" inlet use 40mm all you do is get 32mm clear hose and use it to do the connection between the wavemaker and the piping. If the .4mm gives you hassles on the 1" outlet do the same with 20mm hose.
You will absolutely find a 1 and 1.5 inch theaded fitting at fab, the threaded sides are always measured in inches. Its the glue-in sides that use mm.
I always cut the inlet and outlet holes to 50mm, Fab has a great set of male and female 50mm conectors that work as a great tank connector (ie the fitting that goes through the holes.) up to 20mm bottom glass.
This way you can then very easily reduce the pipe sizes with bushes, cheaply and easily, and you tend not to run into the problem if too small a hole.
You will have no problem Len, whether you want to go rigid or soft piping.
Just be careful the inch sizes are often the inner diameter while the mm sizes we use are the outer dimensions, such as an effast fitting marked as 30mm is actually a 1" fitting according to the markings on the part, I will take a pic tonight if I remember...