My tank takes 3/4" BSPM fittings, but they keep leaking (testing with
air). The trouble is, the fittings don't screw all the way in, so I
basically have to pack them out with loads of PTFE tape to get a seal,
which I'm not happy about. Perhaps that's the way the pros bodge it?

I'd prefer fittings that screw all the way in, but a suitable washer
would work too I suppose. I'm not convinced fibre washers are up to
the job, are they?

Cheers

Tom