  We analyze 45 spectropolarimetric observations of the eclipsing, interacting
binary star V356 Sgr, obtained over a period of 21 years, to characterize the
geometry of the system's circumstellar material. After removing interstellar
polarization from these data, we find the system exhibits a large intrinsic
polarization signature arising from electron scattering. In addition, the lack
of repeatable eclipses in the polarization phase curves indicates the presence
of a substantial pool of scatterers not occulted by either star. We suggest
that these scatterers form either a circumbinary disk coplanar with the
gainer's accretion disk or an elongated structure perpendicular to the orbital
plane of V356 Sgr, possibly formed by bipolar outflows. We also observe
small-scale, cycle-to-cycle variations in the magnitude of intrinsic
polarization at individual phases, which we interpret as evidence of
variability in the amount of scattering material present within and around the
system. This may indicate a mass transfer or mass loss rate that varies on the
time-scale of the system's orbital period. Finally, we compare the basic
polarimetric properties of V356 Sgr with those of the well studied beta Lyr
system; the significant differences observed between the two systems suggests
diversity in the basic circumstellar geometry of Roche-lobe overflow systems
