Lee, I've just been through all this with my Ehiem 2217s. What are the internal dimensions on the intake/outlet that come with your filter?
The intake on mine that went with the 22/16 tubing measured at 17/14 (so 14mm internal diameter). I spent a long time trying to match this without success. The closet I could find was 16/12 or 18/12. I couldn't find 16/14, 17/14 or 18/14. I this the wall thickness is always in whole millimetres. In the end I went with 16/12. On the Eheim the intake is larger than the outlet anyway.