Piece of rubber on the top with a penny on top and a clamp round it?
If you're very good with a drill, drill out the very center to about 3mm go in stages 1.5/2/2.5/3/3.5 then jam in a flat blade screwdriver and "simply" unscrew the remaining bit. This is what I did to the old one(off the car) after replacing the whole hose with a new one for that exact reason.
I'm told the screw is the same size as a plastic number plate screw, but you will also need the tiny rubber sealing ring that goes at the head end of the screw, if you still have the top bit it may still be on it, the clip near the bulk head pipe "snaps" apart but is a pain to access.