zx td fuel filter housing

[8304]

morning everybody,

on the big black zx fuel filter housing there is a white "thing" (its early) on the bottom left looking at the front of the car. It runs inside into the bottom of the filter housing and there seems to be a spring assembly associated with it aswell - it this a 0ne way valve that stops fuel draining from the filter housing back to the tank??
i wonder if this is why im getting air in my system, defunct valve letting fuel slip back to the tank...

what you rekon??

cheers

Alastair.