Originally Posted by Smoketrails
Arriving at F and having to connect to an international flight, you do have the option of not having to go through immigration.
Completely untrue. All passengers must clear immigration when connecting in the US.
Originally Posted by MathFox
The solution to the duty-free-liquid "issue" is to put the stuff in your checked luggage between picking it up at the belt and handing it off again.
The OP is connecting between two international flights and ATL supports ITI bag transfer. The bags will more than likely be ITI tagged in MAN and transferred directly. They will have no access to their bags and will simply show their bag receipt to customs.