My heating radiators have a reducer to 3/4" straight thread. For the 2 holes for venting and the plug I have the proper
Fitting with a soft rubber or silicone ring that makes a seal.
For the connections to pex pipe my plumber tried pipe dope/ teflon tape / pipe dope- Does not work, after a few heating cycles
The connections start to leek. Is there a connector with a flat or grooved surface for an 0-ring available?