  We show that if the inner regions of accretion discs in quiescent dwarf nova
systems are removed by magnetic disruption or evaporated by siphon flows, the
remaining disc is globally stable for mass transfer rates $\lta 10^{15}$ g
s$^{-1}$. This implies that (super)outbursts in these systems have to be
triggered by an enhanced mass transfer form the companion. We suggest that the
lack of normal outbursts in WZ Sge results only from its low mass transfer rate
and that the viscosity in its disc does not have to be few orders of magnitude
lower than in other quiescent dwarf novae.
