I know guys, it's a bit of a mess, stacking ferrules on top of each other. I couldn't find a proper tube, so resorted to amazon.
I know lots of people will trash my install, but you know what? These double ferrules won't go anywhere.
Yes it's not ideal, but I just made it work.
Worst case? I will have a leak, then I'll address it.
I know people are kinda tending to overdramatize it, but you know what?
The original pipe from the pump to the tank had 2 ferrules on each side.
Well, the ferrule on the pump side was metal. The ferrule on the tank size was rubber

so I'm sure this will be fine.
Not ideal but nothing critical I think.