E53 3.0d - Diesel tank not venting

[X-ray Lima]

So I thought my sender unit was stuffed due to inaccurate gauge readings (lh sender was reading full when full (55 ltrs) but getting no lower than 33.8 ltrs regardless of how much fuel was in that side of the tank.

Replaced that sender (original part was smashed at the pivot) and all good for one tank. Refilled and now it's playing the same game (this time stopping at 38.2 ltrs).

Pulled the sender, it's smashed at the pivot - again.

The only reason I can compute is that the tank is pressurising and collapsing in on the sender unit, breaking it.

Now, my question is, which part is responsible for controlling venting to the charcoal cannister? I've had a look at the OEM diagrams and it's not clear to me.

Is there a vent, or is the cannister itself stuffed??

Any suggestions??