I found the adjustable flow risers online. I watch the Blue Angles from my dock. They fly right over the house every year in the same flight pattern. Actually is get's kinda old after the 3 days of practise before the show.
PS.
They are called areator heads and you can get them in different lenghts. If you use a 1/2" high speed pick up you can easily use a 1/2" FIP x Socket PVC adapter to screw on the ends of the 1/2" male threads on the pick up. Glue on a short piece of 1/2" PVC, a ball valve, then a 1/2" PVC riser and cap the end. Cut slots in the PVC and your done.
Or a 1/2" threaded PVC ball valve screwed to the 1/2" high speed pick up. You would have to thread the valve on the male ends of the pick up before mounting the pick up to the box.