I think I now understand. Kind of like a slide trombone, so to speak.
Actually, you could remove the thin tube altogether, and wrap a layer or two of Electrical Tape around each of the 2 ears of the pressure sensor unit to thicken it up. Then, it would be a press fit inside the 1-1/2" PVC pipe to hold it securely in place in the new filler tube.
Raybo