Coolant leak

[Gibboian]

Having replaced the chain and sprockets at the weekend I made a school boy error and omitted the cable tie that keeps the hoses out of the chain... Doh..  So now I need to replace the hose that goes into the back of the engine.

Does anyone know the part number? (2002)

Also,can I just top up the coolant through the top of the radiator? Will it flow into the expansion tank to get the level?

Any other good ideas accepted.