"Dan Luke" writes:

Remember that in Larry's example the water is distributed among four
tanks. 2mL split four ways ain't enough to worry about.

Perhaps (though others' tanks are much bigger). But as to how such
freezing could happen, consider (not) topping off on such a warm day,
and climbing to 10000 ft for cruise. That temperature drop might be
all you need to freeze out the water. It's not only during winter
that this may be a consideration.

Can someone imagine a scenario where over several heat/cool fill/fly
cycles such ice could accumulate? Perhaps failing to sample the fuel
bowl/drains over several consecutive flights?

If it freezes will it float in avgas or stay on the bottom?

The density of avgas is around 0.7 g/mL, water 1.0 g/mL, ice 0.9 g/mL.
Ice would still drop to the bottom.

- FChE