Are you sure what you are hearing isn't just the horrible phasing and dispersion characteristics caused by laying an 8x10 on it's side? Oh, wait... This isn't the amps forum, is it?
But seriously. I hear him playing with what's either a short delay or a really tight reverb at the breaks and adding an octave down to it at 2:20. IMO, what sounds like a filter is really just a combination of his touch, a fretless and a heavily driven amp.
Here's a link I found with better sound quality. http://www.youtube.com/watch?v=0Rkv8ZuAmO0