This adapter couples a 2 1/2" power tool vacuum output to a 1 1/4" vacuum hose.
If you need a more durable part or your thin walls are prone to delamination, consider my Industrial Vacuum Adapter 2 1/2" to 1 1/4".
Optimized for 0.40 mm nozzles. Wall thickness is 1.6 mm so it has 4 shells on most layers. That keeps the print head moving in smooth circles.
For this application I prefer the flexibility of ABS. If you print in PLA, try scaling to about 99.5%. Save some filament by printing the test file first. It is the top and bottom 2 mm of the adapter.
Also, consider adding a skirt of 8-10 perimeters touching the part so it won't lift off the print bed.
Scrape the bottom edges smooth with a hobby knife.
Acetone vapor bath for strength is optional.