Rusty Tanks? Sounds like a Blues singer.
And if you leave the rust to spread, the blues is what you'll be singing.
Takes me back to when I was 18 or 19, riding a '58 Triumph Speedtwin. My mate and I were on our way into Hereford, the traffic was backed up a bit from the roundabout and we were busy swerving our way through when he came alongside me, on his Stan Stephen's Stage-3 tuned, RD350 YPVS, to tell me that I had a water leak.
My initial response was "F#ck, where from?"
It dawned pretty quickly that there is no water in a pre-unit Triumph! The tank had split and petrol was absolutely pissing out all over the head and barrels! I killed the engine, which helped a little because the vibration stopped, and calmly pushed (very quickly) it over to the bike shop that used to be on that very roundabout. A mechanic there gave me a tray to put under it, and my mate gave me a lift back home where I borrowed a Transit from work to pick up the old Trumpet. Job's a fish.
But I digress, as usual, because we're now in Bandit country. One of the first things I noticed about the Bandit was the fuel gauge, and it didn't move as Suzuki intended. There was also rust visible in the tank.
A quick test of the fuel gauge goes as follows: unplug the tank sender unit, rear right of the petrol tank on the Bandit, and insert a wire into both terminals of the loom. This is basically returning 12v to the gauge (or mimicking a full tank). The gauge went to the full position so happy days. Time to pull out the tap and fuel sender.