[BigOz]

Having done a few weld repairs to Ducati tanks I'd urge you to decide if the tank needs metalwork before applying a liquid fix or sealer.

I've had a couple where fixes were attempted in this way and it causes problems,nothing that can't be worked around but in one case it took ages to clean up the metal around the repair to avoid contaminating the weld.
Trying to remove an epoxy like finish without further thinning the already thin metal though a small hole in the tank is not fun and will cost an arm and a leg if you're paying a professional to spend the time.

I'd start by draining the tank and get a good look at the area from the inside, you might need to get a cheap inspection mirror and torch/light source you trust not to ignite the petrol vapor to see around the inside of the tank though the filler hole.

If it is going off for welding strip the parts off the tank, filler cap, pump e.t.c. so it is as open as possible and leave it somewhere warm and well ventilated and away from ignition sources (outside in nice warm sunny weather is good) for at least a week before handing it over to someone and warn them that it is a used tank that has and may still contain fuel no matter how obvious that might seem.