  We investigate the weak-interaction-driven bulk-viscous transport properties
of $npe$ matter in the neutrino transparent regime. Previous works assumed that
the induced bulk viscosity correction to pressure, near beta equilibrium, is
linear in deviations from the equilibrium charge fraction. We show that this is
not always true for (some) realistic equations of state at densities between
one and three times saturation density. This nonlinear nature of the
perturbation around equilibrium motivates a far-from-beta-equilibrium
description of bulk-viscous transport in neutron star mergers, which can be
precisely achieved using a new Israel-Stewart formulation with resummed bulk
and relaxation time transport coefficients. The computation of these transport
coefficients depends on out-of-beta-equilibrium pressure corrections, which can
be computed for a given equation of state. We calculate these coefficients for
equations of state that satisfy the latest constraints from multi-messenger
observations from LIGO/VIRGO and NICER. We show that varying the nuclear
symmetry energy $J$ and its slope $L$ can significantly affect the transport
coefficients and the nonlinear behavior of the out-of-equilibrium pressure
corrections. Therefore, having better constraints on $J$ and $L$ will directly
impact our understanding of bulk-viscous processes in neutron star mergers.
