I think the pump is 70 LPM. The pipe work is 22mm. I thought about going for 28mm, but that creates its own set of problems. A mate of mine made the bends for me, and doesn't have a bender for 28mm. The valves are a good bit more expensive, as are the fittings, and I don't have a big enough drill.
So all in all, although I would have liked to use 28mm, I decided on 22. It will give me a chance to learn the ropes, I can see that it won't be long before I'm thinking about building another one anyway................