Yes the clear one that I fitted when we were looking for the air. If you remove the one at the tank end, but leave the one at the lift pump, it will tell you if you have air in that line still. It won’t be as exact as if you leave it fitted, but it will still separate the fuel system into a much smaller section if you need to fault find again.
If you don’t want to remove it, try and arrange the pipes so they are on top of the chassis rail, and not kinked at all. Then secure them.
