I took my 2003 disco2 gas tank out to fix rear frame rails.
I noticed a cheap black plastic tube inside the filler tube that seemed like it was just slipped over the inner steel tube inside the gas tank filler tube.
Was this suppose to have a clamp on the inside pipe? The outer rubber hose did have two clamps holding the larger outer tube secure.

When putting the pump back in the tank, how do you fit the rubber pump gasket?
Should I place the gasket on the tank first then insert the pump?

 

Looking at the photo of your tank I don't see the breather pipe that is shown in RAVE. RAVE shows it exiting the tank roughly in the centre of recessed section of the tank. If yours doesn't have one there then it is likely that the tube inside your filler pipe is an internal breather. Have to admit that when I last had my tank out my breather was on top, but I'm in the UK and in the US you have some differences relating to emissions.

 

the inner hose has no clamp it just side of the tube in the tank.

fold the gasket in 1/2 then open when inserted in the neck of the tank,put a little gas on the gasket and slide the new pump in.