"But the Sierra does have in in tank pre pump filter, its in the middle of the plastic swirl pot"
No swirl pot in my sierra tank, I looked, and it was out of 2.0i. I could see nothing in the outlet pipe and I shone a torch into the sender hole to see! There was definitely no pre filter!
"If you'd seen how many filters were inside a petrol pump, you'd know that the debris didn't come from the pump."
As for the dust and dirt I can only think it must have got in between tank fitting and finishing all the initial plumbing, in hindsight that is perfectly possible given the way the wind can blow debris under my garage doors! Isn't hindsight wonderful? Still, once all my bits arrive, a good blow job on the tank and a pre filter should help!