Stains from the water inside an orange hot water bottle - any ideas?

[BranchingOut]

I have an item of clothing that is stained by some water that had been hanging around inside an orange hot water bottle.

Any suggestions?

OK, well clearly this is too bizarre for anyone else to have had this problem!

Napisan?

Thanks, what does Napisan do?

If it's water that's been exposed to rust I'd squeeze juice of half a lemon on it.

Think napisan is a type of stain remover.

Not so much rust as rubber.