Gatorade bottles, and a lot of caution trying to keep the plane under
control and not get wet pants ... That's what I use. I have often though
about the venturi idea. It isn't far fetched, the Grumman E-2C's I worked
on in the navy had a system for exactly that. With a relief tube at the pilot/copilot seats.
The Gatorade bottle system works better in summer than winter, since
here near Chicago means multiple layers of clothes, which complicates
things ...
Jeff