I'm surprised to hear that anyone would want to run their fuel down to the dregs. The reason being that the A2 is not a new vehicle so there is years of all kinds of build up in a tank. I used to work for an independent fuel & oil supplier and we would pick up fuels from Manchester Fuel Terminal (MFT) and Shell Stanlow, Cheshire. There would be Shell tankers before and after our vehicle and the notion of the fuel being different could not be further from the truth, we also loaded up alongside the major supermarket tankers. So again everyone was taking the same fuel to the same specifications.
Shell were a bit naughty as their fuel came out warm from the refinery and cooled overnight. Some fuel stations complained that they we're loosing up to £30K / year due to the specific gravity when sold ment that the temp difference ended up with the load being short.
In winter 200 LTRs of Kerosene would be added to 17,800 LTRs of diesel or as the owners said Winter fuel.
We also stored fuel at our site in silos, but in summer when quiet the silo would be run down and the service plate opened, and here's why you should not run your fuel down to the dregs. You would have to shovel out the algae that had grown in-between the fuel (oil) and water. The water is there from condensation and most A2's have had15-20 years for it to build up in the tank. There was other debris that had got past filters as well another reason not to find down the fuel to nothing.
On the oil side that was similar in that the oil is made to a specification so as long as you go for the same spec you should be OK. I have been using oil from Westway Lubricants in the Midlands and just bout 20 LTRs of the correct spec for one of the cars for £65.
A bit of a story but that's what happened.
Take some photos of before and after of the inline fuel filter when you have done your diesel purge.