We have studied dielectric relaxation in liquid-impregnated porous solids. The samples were constructed from either glued sand grains or sintered polypropylene beads. We experimentally obtain two relaxations originating from the bulk of the sample. Electrode effects are seen at low frequencies, only for high liquid conductivities. The two bulk relaxations are interpreted as being due to diffusion in the electrochemical double layer surrounding the solid grains, and as a Maxwell-Wagner relaxation due to the heterogeneity of the samples, respectively. The experimental results can be qualitatively reproduced by calculations using the grain consolidation model, which was extended to take into account interfacial effects. The permittivity at high (megahertz) frequencies can be understood by using simple mixing laws. We also propose an equivalent circuit for the electrical properties of a liquid-impregnated porous solid.