If you’re getting a lot of melted spice in the lower portion of the pipe directly below the screens, then maybe your screens/mesh aren’t sufficient to hold the liquid. Maybe add a few more screens or make your mesh disc a bit thicker.

If you’re talking about residue near the curve of the pipe, that’s from condensation, and I don’t think you can do much about it – when hot vapor hits comparatively cold glass you get condensation. However, I’ve noticed that condensation seems to be less of a problem if I clean my GVG frequently. It seems that once the inside glass surfaces have a coating of condensate on them, future condensation forms more readily.