Hi Rob
Not sure if it is the same across all models but i fitted a pump to our 14 and the pressure line that jaco used was 12mm. Got mine from here and the fittings here . Didn't touch the drain but from memory it looked closer to 25mm than 20. could be wrong there though.
Bring your van down to the meet at Canungra this weekend and i will get chartrock to crawl underneath and measure it up for you.
Thanks very much boots, that JG system looks excellent, I'll use it for this install. Thanks for the offer for this weekend, unfortunately I am on call. I will crawl under and work out the drain pipe as I need to get a better understanding on all of the Van systems as we will be working in remote areas and will need to be able to address issues that may arise. I'll post back some data and pictures when I'm done incase anyone else wants to do the same.