Planar close top and bottom of bottle.
Select horn and rename horn1.
Select other horn and rename horn2.
Select all, and deselect horns, rename basebottle.
Boolean difference and select basebottle, then horn1.
End up with a hole.

I thought that there would not be a hole?

If you form a solid cylinder and do the boolean difference, with a horn,
there is not a hole, just a cylinder with a scoop shaped portion removed.

So the bottle must have a defect/ not be watertight?

Burrs method works, but why? There are two planes formed at the top,
and two planes formed at the bottom.