A cap-free filler neck for a motor vehicle tank comprises a tubular part, which is connected to the tank, and an insert, which insert comprises a funnel part with a throat and a partition part adjoining the throat at the bottom. The upper edge zone of the funnel part and the partition part adjoin the tubular part in a sealing manner. The partition part has a throughflow opening which is closed in a sealing manner by a flap, which can be locked in a closed position, and can be pivoted into an open position counter to the force of a spring by a fuel nozzle. So that, despite the tight closure, rainwater which has penetrated can flow away, the space delimited by the tubular part, the funnel part and the partition part can be brought into connection with the environment via an opening in the tubular part, which opening can be closed by a valve, which is accommodated in said space, by the introduction of the fuel nozzle.