improved devices , systems and methods for treating a tissue region provide straightforward , yet reliable ways for installing diverse functional components within the confined space of a catheter - based instrument . methods include providing a manifold body sized to fit within a catheter tube , the manifold body including a single main fluid junction , multiple branch fluid junctions , and a fluid circuit formed within the manifold body to channel fluid flow between the single main fluid junction and the multiple branch fluid junctions , coupling the single main fluid junction to a fluid source or a fluid destination external to the catheter tube , coupling each of the multiple branch fluid junctions individually to a fluid - conveying port on the operative element , and mounting the manifold within the catheter tube .