I know your site has warned against lining the waterline and I am not sure but I think tightlining is basically lining the upper water line or is it something different I'm not sure. Heres an article explaining what it is and how to do it: http://www.beautylish.com/a/vmqmg/how-to-tightline-eyes
What the article shows is actually filling in the gaps between the lashes. So you are not actually lining the waterline. That never stays put anyway. Please note the link in that article that recommends cleaning your eye pencil before doing doing this. I had never heard it called tightlining before, but I have seen it demonstrated by several different makeup artists.