When I put my bike to sleep of the winter months
I put half a bottle of Wynns dry fuel in the tank.
you can get it from Halfords or other motor factors.
Bikes (cars to for that matter) can pickup a surprising about of water in the tank over time.
I have seen some people get about half a pint of brown rusty water out a bike tank and that's from a bike used daily, never mind
one stored.
that's why I first used the Wynns stuff on my bike when I first got it, just to make sure it was clear.