Inline Filament Dryer [video]

there have been a lot of inline filament drying methods tried. I experimented with a lot of the earlier attempts.

they all work fine-ish for non-engineering materials; the problem of course is with the very hygroscopic materials that suffer permanent damage and deformation after water incursion.

nylon, polycarbonates, PEEK, etc : if you let them get contaminated with water generally only black-magic print settings can get them to come out decently -- and even then there is evidence of bubbling/bursting upon destructive teardown and metrological inspection; so if you're printing customer work that has a strength expectancy -- well, it's trash.

The only real method is to keep the material in good shape from the get-go. The band-aids all suck. Remember, the water can literally move and deform the plastic, when the water is removed the deformation isn't necessarily -- and if it has changed it likely hasn't follow the same symmetry as when it was extruded from the plant; this will of course at the very least affect your extrusion mass calibrations -- and in a dynamic and unpredictable way. This is probably fine for 95% of hobby DIY projects, but not for those that need extrusion accuracy.

Buy small quantities, store it well, and ideally live in a dry place. Put the filament away when you're done using it, and consider the (very small) investment of a vacuum sealer and a box of desiccant.