18 months sounds good, i thot of cleaning and rebuilding the loop every 6 months, maybe ill postpone it a little.

Im also using Tygon and PC Ice no dye, well actually i got the Invisible Blue which looks clear but supposedly turns UV Blue under UV...but somehow I didnt see any UV. That aside no complains.

On a side note, I just got hold of a TFC 240, the TC does look to be more solid tho', plus the TFC has a hollow sound when i knock the sides, iinm i read someone here with the same experience.