Mark if you use a 3/16th inch tube between the walls the fit is tight enough to secure it. you can also use a piece of glow fuel blue fuel line around the outside of the tube and wedge it between the pipe at the back. it will stand up to the heat. I also use a one way check valve. I found that the pressure from the tail pipe will actually cause the smoke pump to lose its prim in flight. I also set up a header tank so I don't get the negative G on and off smoke through maneuvers.

Joe L.