1. Make sure you have installed AVISynth plugin when you install ffdshow. Look for "ffavisynth.dll" in the AVISynth plugin directory.
2. Under "Image Settings" of "Video decoder configuration" of ffdshow, add a new preset "5-Tape-Deint", which enables the 5-tape deinterface filter only.
3. At the start of your AVS script, add loadcplugin("ffavisynth.dll")
4. Then at the appropriate place, add ffdshow(preset="5-Tape-Deint")