In my personal experience, you can blow in them, but it takes zero air flow to make it spin fast. So just barley blow. No air compressors, canned air, etc. Just a very light breath. Remember, these things put out 30-60 thousand pulses per gallon, so if you empty your lungs into them that's about 2 liters of air in just a few seconds instead of 4 liters over 3 minutes.
In all reality, no harm in pouring some water through it either. They are all aluminum and plastic so no rust issues. Assuming you leave it sitting around for a while so there is no liquid water left inside when you go to bolt it to the fuel system.
Finally, if all you are testing is wiring, you can just short the signal wire to the ground wire and tap it quickly. This will show flow on the EFIS and you know at least your ground and signal wires are right. You can measure ground to power to know it's right. At that point, all that can be broken is the flow sender itself, which would be tremendously unlikely.
But if it were me, with my plane, I would just bolt it up, wire it like it says, and go. This really isn't something you need to test while installing.
--Ian Jordan
Dynon Avionics
