  We study distributions of dissipative and nondissipative avalanches in
Manna's stochastic sandpile, in one and two dimensions. Our results lead to the
following conclusions: (1) avalanche distributions, in general, do not follow
simple power laws, but rather have the form $P(s) \sim s^{-\tau_s} (\ln
s)^{\gamma} f(s/s_c)$, with $f$ a cutoff function; (2) the exponents for sizes
of dissipative avalanches in two dimensions differ markedly from the
corresponding values for the Bak-Tang-Wiesenfeld (BTW) model, implying that the
BTW and Manna models belong to distinct universality classes; (3) dissipative
avalanche distributions obey finite size scaling, unlike in the BTW model.
