Searching for the location of a slow but persistent pressure loss in our home’s hydronic heating system, we'd like to isolate one zone at a time from our Watts Flowmaster Radiant Manifold and monitor the pressure in the remaining system for a week or two during the warm months. We have the #81005470 3/4" BSP caps and gaskets to seal the two exposed manifold ports. To preserve as much of the treated system water as possible, we wonder if there is a way to seal each end of the Pex connections we'll be removing? Referencing Watts' on line product catalogs, it appears that the female threaded fittings that screw on to the manifold retain a cylindrical brass insert (which is connected to the end of the Pex tubing) that seals inside the bore of the protruding male portion with an "O" ring. We'd appreciate any suggestions for somehow plugging each of these threaded-cap-and-insert ends to retain the treated water in the disconnected zone. Perhaps you could suggest a combination of fittings we could use to fabricate two such plugs.