  The continuous emanation of $^{222}$Rn from detector surfaces causes the
dominant background in current liquid xenon time projection chambers (TPCs)
searching for dark matter. A significant reduction is required for the next
generation of detectors which are aiming to reach the neutrino floor, such as
DARWIN. $^{222}$Rn-induced back\-grounds can be reduced using a hermetic TPC,
in which the sensitive target volume is mechanically separated from the rest of
the detector containing the majority of Rn-emanating surfaces. We present a
hermetic TPC that mainly follows the well-established design of leading xenon
TPCs and has been operated successfully over a period of several weeks. By
scaling up the results achieved to the DARWIN-scale, we show that the hermetic
TPC concept can reduce the $^{222}$Rn concentration to the required level, even
with imperfect separation of the volumes.
