This is my first post on the website and hope it gets out.  I have just watched an episode on TV and saw that the figure-8 knot shown was tied completely wrong.  The knot on TV was only half a figure-8 knot, so of course it slipped.  From previous articles in magazines I remember the improved clinch(trilene) knot is about 90-95% the strength of the line.  The figure-8 and palomar knots are 95-99%. 

The way you tie the figure-8 knot is too make the knot like shown on TV except the eye of the hook goes on the tail of the shown knot, then back up to the already 1/2 figure-8 and the line follows the line back through the first 1/2 of the loop.

Here is a link that shows how to properly tie the figure-8 knot..

Hope this helps.

http://www.indoorclimbing.com/Figur..._Knot.html