To be honest, I doubt that drainage will help: if there is a connection, it should be draining quite low from Pant Mawr; otherwise it'll come out of the bottom of Moelwyn itself.
The vein at Moelwyn seems to be quite vertical and there may be an issue with the connection (if there is one) being on the wrong side of a deep hole!
I'm tempted to suggest that the more interesting route may be into the top of Pant Mawr and then down to one of the lower adits - I doubt there's a connection to Fron Boeth, but there have to be some way into the upper levels of Fron Boeth which can be seen from the lower level.
Incidentally, I don't suppose anyone has a survey for Pant Mawr / Fron Boeth lying around? :angel:
I did have a plan of Fron Boeth and pant mawr including the tunnel. It was given to me by the late Griff Jones that wrote the book on Rhiwbach and Cwt y Bugail etc.
I have had a look, but cannot find it.
Fron Boeth is basicaly 3 to 4 levels with most of the chambers at the lower level where the boiler is. You can see down from the upper levels down to the bottom. Very interesting artifacts there. The mill area is well worth a look around.
Pant mawr has not a lot to offer and is not connected to moelwyn as far as I can tell.
It might be possible to get a copy of the plan from 'Plas tanybwlch' as Griff was very involved with the place.
Bellach dim ond swn y gwynt yn chwibian, lle bu gynt yr engan ar cynion yn tincian.