PortageKeeper: "I made the same one from a trash bag for a ul inflator - works great!"
Yes, before I put a hole in my dry bag I made one with a trash bag to see if it was practical. The trash bag inflator I made is next to the sleeping pad valve in one of the photos.
I also used a vacuum seal bag to make one. It holds a large volume of air and inflates quickly but Is too bulky.