  In order to prepare the ground for evaluating classes of three-loop
sum-integrals that are presently needed for thermodynamic observables, we take
a fresh and systematic look on the few known cases, and review their evaluation
in a unified way using coherent notation. We do this for three important cases
of massless bosonic three-loop vacuum sum-integrals that have been frequently
used in the literature, and aim for a streamlined exposition as compared to the
original evaluations. In passing, we speculate on options for generalization of
the computational techniques that have been employed.
