[sunman]

Pull the line from the neck fitting, add a 3’ piece of tubing with a short piece of pipe and blow. Simple line check.

My sender flange has a top of tank fitting and a fuel return to a baffled well in bottom of tank fitting. I EFI modified my CR steel tank (future thread).
Check that the filler neck line does run to a top of tank fitting.

When you blow with the cap on and neck fitting plugged the EFI fuel system should be sealed when the new tank is installed.

There is a bung on the filler connection side of BDR aluminum tank, but it looks to low to be a top of tank fitting.
I’m not familiar with BDR tank, is that bung a bottom of tank fuel return from regulator line fitting?