I have cleaned out the fuel tank in my D & F roadster. I poured in a few pounds of square carriage bolt nuts and couple of hundred tek screws and proceeded to rock the tank to abrade the loose rust on the bottom. It took about two hours, on and off, before most of it was removed.
Then I had it grit blasted snd gave it good coat of spray on galvanising paint.
The spout arrangment is to allow filling through the trunk.
The tank is fitted behind the seat, in the turtledeck.
To compensate for moving the tank further to the rear, it is mounted on a pair of blocks. With the thickness of the body base and the floorboards, the tank is effectively raised a bit over 4" over the stardard level.
The car I am using as a reference fot other work, has its fuel tank suspended under the spare tyre carrier, so it has vacuum tank on the firewall to draw up the fuel.
Allan from down under.