I have tested around with Fluid piping from forge to Fabric and vice versa.
I thing #4 is not finished?

It would be great if the interaction could be improved.

What mods are you using? How can I reproduce this issue? Please provide more information

I've used EnderIO (Forge) and Industrial Revolution (Fabric)

##Screenshot description:
on the bottom left, it works:
IndRev Tank -> Indrev Pipe -> EnderIO Tank
the other direction does not work.

on the right, I have the same setup, but using Fluid Conduids
I have checked a few minutes a go, all my mods are up to date.