Should go in as per instructions (if not get your dremmel out). My first SE, I used the supplied World Models tank per instructions - stopper was made of a poor quality material and leaked after a year (made a real mess inside the fuse). My current SE has a ten oz Sullivan round tank in it - only needed some minor mods to the plywood formers inside the fuse (dremmel). I can now fly my Saito 72 equipped SE for 20-25 min!