Hey Jim, Is the saw dust under the tape or over the tape? I don't see any reason to use multiple layers of tape. If you don't apply the tape correctly saw dust will accumulate under the tape and obscure the line. I use a plastic putty knife to burnish the tape, that is I rub the tape with the putty knife to make sure it is tight to the pattern. If the dust is on top of the tape, then try to adjust the air blower hose closer to the line.
If that does not help, then switch to a skip tooth or a reverse tooth blade.