18k 2 Owner Trident 900

Hey classics dudes.

I always wanted an old 900 Triumph. Had the 1050 speed, Daytona 955i and a 675 Daytona.

Today I took 3 steps closer to owning one.
Contacted one seller had for sale, HPI checked it, and plucked up the courage, and rode over to take a look. The owner was in France but his son in law is selling it for him.
It's all perfectly above bord.

Looked dirty but i can see it has great potential to clean up like new.
On inspection the battery was dead.
It had been stood. The owner had 10 years and not used it much.
The son had gotten a garage to pick it up, MOT it, and the garage guy rode it back to his house. Only needed fork seals and nothing else.
I asked if I could look in the tank and found a red coating inside it and around the filler neck. It didn't rub off like a powder. I put a stick in the tank to rub a patch off but it wouldn't come off. The fuel was fine and it left no residue on the stick.
The owner had cleaned the carbs out before sale. He's a mechanical engineer and works on tractors.
So it's never needed for anything.

My question is, what's in the tank??

 

Haven't a clue?
Must be.
I've seen rust in an old triumph trophy sports bike. So roughly know its not rust. Just can't be sure.

 

I'm going to run away as fast as possible I reckon.

 

I've been informed...

New message from a seller on ebay...
They have one on ebay like it.

The red you can't see is the red liner triumph fitted to all early tanks, there is no serious rust on this tank