Eb2-F2. Christlieb, Don. Pictoral Fingerings for Bassoon. Published by author, 1966, p. 19. Timm, Everett LeRoy. The Woodwinds; Performance and Instructional Techniques. Boston: Allyn and Bacon, 1964, p. 171.
"Clumsy, but in tune." Trill D and E keys together:
Eb x x x | x x x F E-tr D-tr
"The F is flat." Cooper p. 12.
Eb Db x x x | x x x F w E-tr D
Heckel-System (German) Bassoon Trills and Shakes by Note Names