I bought this dual body regulator, and it has a hard white plastic washer threaded into the inlet side. Do I need to add an additional washer -- either black grommet (like on the beer lines) or the cardboard washers that some tanks have -- or can I just connect it as is?
The stock washer should do just fine. If it leaks, then worry about it. You may need to replace it now and then, I don't know too much about those built in washers.