Print the main model and the adapter for the fan type you want to test. (There's only a 5015 adapter right now, I'll add 4010 and 4020 soon)
Fill partially with colored water, maybe halfway. Don't fill too much or the water will spill out when you turn on the fan
Screw in adapter onto one arm
Turn on the fan and hold it on the adapter. Press down so the air doesn't leak too much.
Measure the difference between the water levels in the two arms. That's your static pressure (in units of water column). The big divisions on the manometer are 1 cm and small divisions are 5 mm
Print settings
All files in correct orientation for printing
Print with 0.12 mm layer height for better threads
Increase flow by 1-2% to make sure everything is water tight and to make the print more transparent
If you want tips on how to make your print more transparent, watch this video. But it should be fine as long as you can see the water level.