Maybe belongs in th The fix is in thread, but, anyway.
Read at multistrada.net about some trying to dry out tanks to shrink.
I had a go at it, gave it 3 months.
Removed pump, had an old PC HD fan in the pump cavity 2 of three months, open cap all the time, done in dry room temp garage.
Bit hard to measure but tank is about 3 mm shorter!
Can remove and refit with just hands, gone are any tools+violence.
Very pleasing for the soul.