Unless I've missed something, we've all been offering feedback and advice without knowing exactly what instrument is being played. What does "bass trombone" mean here? While most of what's been said is reasonable for most "generic" bass trombones, there can be some differences among the single-valve horns, the independent double-valves, and dependent double-valves. And a lot of people play the "bass trombone" part (or maybe just 3rd trombone part) on a large bore tenor (like a Conn 88H -- which, when I was in high school, was actually considered to be a bass trombone). When I hear "bass trombone", I think "double valve" and .562-ish bore since that's what I play. But there's a lot of variation around -- as reflected in Aharoni's book and treatments of some of the current possibilities.
Gary Merrill
Wessex EEb Bass tuba (DW 3XL or 2XL)
Mack Brass Compensating Euph (DE N106, Euph J, J9 euph)
Amati Oval Euph (DE 104, Euph J, J6 euph)
1924 Buescher 3-valve Eb tuba (with std US receiver), Kelly 25
Schiller American Heritage 7B clone bass trombone (DE LB K/K10/112/14 Lexan, Brass Ark MV50R)
1947 Olds "Standard" trombone (Olds #3)