  We demonstrate that the source to target mean first passage time (MFPT) is
approximately given by the potential difference of an electrostatic problem
which shows that the MFPT scales like the resistance between the target and a
distant shell. This analogy allows the asymmetry of the MFPT on non uniform
lattices to be incorporated and provides a number of useful insights. For
example, on transient lattices, the MFPT converges exactly to the product of
the mass and the site dependent resistance between the target and a shell at
infinity.
