I put that tank in 9 years ago, so forgive me if I don't remember what size it is, but if I had to guess, I'd say 10 or 12 oz. I have the tank shoved back into the radio compartment, and an 8 oz smoke tank where the fuel tank should go. The pump sits under the tank tray, and both battery packs (radio and smoke) are in the aft Fuse.

Years ago in a minor crash, the bottom sheeting under the tank (forward of the main gear) ripped out, so there is a big open space there for the pump to sit. I'll try to remember to take some pics of it.