Testing my new heavy launcher design

[Kottabos]

So after several missions that either failed or were far too close to failure due to fuel I decided I finally needed to build a larger launch rocket to get larger payloads into space. the following video is my attempt at testing this new design of mine:

as you can see, a few things went ... shall we say poorly. I am having issues with my fuel lines moving fuel between tanks which honestly I'm having a hard time figuring out. the first 2 section detach fine after using up their fuel, but the final outer layer to seperate just doesn't want to cooperrate. I would love any tips/suggestion you guys have as I could really use some help on this. Thanks for reading/watching my friends, and thanks for any help.

[carazvan]

The problem is that under high thrust the link between the orange fuel tank and the smaller fuel tank separates on one of the outer engines (that's why it stars being unequal in fuel usage - you basically lose an engine and it just happens to "stay attached" because it's pushing on the base of the orange one).

You can cut back on thrust to mitigate it slightly but more certainly use struts between top of white 32 tanks and orange tank