In the late 70's, while working at Rocky Mountain National Park (Estes Park, CO) I was doing flight training in nearby Longmont. I also scattered ashes over the "Front Range" on several occasions to earn money for flight time.
On the first scattering job I flew to the appropriate location and got ready to do-the-job. I got everything ready, uncorked the urn and opened the window, and moved the urn toward the open window. That's when I learned about something like the "venuri effect." In an instant a smallish quantity of "uncle Fred" was swirling around the inside of the small Cessna 152. Happily, about 90% of "uncle Fred" got to his intended destination ... but the remainder took a while to clean-up the interior when I returned to the airport.
I learned that a preferred technique was to extend the CAPPED urn outside the open window THEN remove the cap. Live ... and Learn!
Best,
C&M