The existence of submerged components can significantly influence the seismic response of a liquid storage tank. Consequently, due to the modification of dynamic properties, the seismic behavior of liquid tank systems with internal components can be significantly benefited. In this research, a potential-based finite element technique has been adopted to study the slosh dynamics of a partially filled rigid rectangular container with a bottom-mounted submerged block under harmonic excitation. The liquid domain is governed by the Laplace equation where a velocity potential-based Galerkin’s approach is adopted for the liquid domain formulation. The obtained results of the developed finite element model are validated with the published results with a decent agreement. The phenomenal sloshing behavior of the base-isolated tank for different widths and depths of the block is emphasized in the present analysis by the application of the laminated rubber bearing. The parametric research of tank-liquid-block-isolation systems demonstrates the significance of varying dimensions of the submerged structural component.