2002 Vauxhall Corsa 1.2 petrol leak?

Vauxhall Corsa 1.2 (2002) has a petrol leak. It does not appear to be the actual tank itself, but what might be a type of "inline filter" which looks as though it attaches to the petrol tank. Do you have any diagrams, or advice as to what this is called, and how to get at it.
Thanks