I don't have a Hanson UAT so I don't have any first hand experience with them. My advice is to remove whatever that black thing is in the cap. If you look at Hanson's ad he doesn't show any cap seal. Those Nalgene caps have a built in lip seal and any additional seal is not necessary.

Make sure that the top of the bottle and the cap will contact evenly all around the circumference. Check it with some air pressure before trying to fill again.

Joe