Hi forum
I'm resurrecting this 1989 k100rs and the original pump and all the internal pipes had dissolved and turned into black slime.
I ended up using a subaru forester xt fuel pump that I had in the shed and still have the inline filter, that works after I'd took the return valve off and cleaned out the corrosion.

I get the dribble catcher at the lid to drain away any fuel spilt but what is the other pipe?
It's near the front of the filler and is curled downward.

I put a bit of hose with a bolt in but this morning the bolt is in the bottom of the tank like was sucked out.

Thanks in advance.

Skidmark wrote:I get the dribble catcher at the lid to drain away any fuel spilt but what is the other pipe?

Take a look here.

It's line that goes to the fuel pump screen, I don't have that anymore. Also my return seems to jet fuel forward to the front of the tank. Does that fatter tube become pressurised? And the pipe to the pump screen just feeds the pump with returned petrol?
I will take a better look In the tank tomorrow, if it ever stops raining.

The fatter tube doesn't get pressurized. It's a chamber that serves to depressurize the tank by routing air, fuel vapor and excess fuel out of the tank. The hose from the screen filter doesn't receive fuel. It evacuates air bubbles that otherwise might enter the pump and damage it. The main cause of that would be running the fuel level in the tank low enough that it gets agitated during intake. That hose has been absent from my Brick for 60K miles—no problem. Your Brick's return fuel is likely coming from a pipe in the forward tank floor that's likely attached to a check valve at its floor connection. Later models had return fuel cascading from a pipe routed above the fatter tube—a tube referred by some as the burrito.