Found something which works.
I found from the US supplier that the opening takes a standard left hand threaded vacuum hose. Thought there is no standard
I decided to do some searching so this afternoon I went to a local vacuum cleaner sales and repair and found this
It works really well when fitting into the router opening though Screws in easily enough but appears to have a great seal. I didn't take a decent picture. You can see that if fits all the way in the opening but stops before entering the bit area upper right of the picture.
What I bought was one foot (to test) from what the vendor had as "cut to length".
I did a search and found this picture which closely resembles the piece I have.
It is a "Filter Queen" reinforced hose"
I paid $2.25 for one foot so tomorrow I will go back and buy a 6' length which should be about right for my under table needs.
I still don't have a fitting for the other end, but that should be MUCH easier.
My "assistant" in making the 3d print has taken off on vacation for a while and I am lost without his help so I will abandon that direction for the near future and stick with this hose.
Hope this helps.