This work focuses on the analysis of the Casimir effect for pistons subject to transmittal boundary conditions. In particular we consider, as piston configuration, a direct product manifold of the type [Formula: see text] where [Formula: see text] is a closed interval of the real line and [Formula: see text] is a smooth compact Riemannian manifold. By utilizing the spectral zeta function regularization technique, we compute the Casimir energy of the system and the Casimir force acting on the piston. Explicit results for the force are provided when the manifold [Formula: see text] is a [Formula: see text]-dimensional sphere.