Quote Originally Posted by Vern View Post
Back to this, how does fuel get into the canister?
There is a non-return valve under the fuel return pipe. Return flow from the engine causes a jet pump effect sucking fuel in via the non return valve. This way the pot is always full and the (petrol) pump remains fully submersed. Also it keeps a small reserve when the tank is nearly empty and you have fuel slosh away from the pickup.

I have no idea if the diesel's return flow is enough to activate the jet pump function. You would have to inspect a 300TDi assembly to make sure.