I did a test of munton's dry yeast to make sure I could do it. My first "test" of yeast washing was tough because I too couldn't tell a difference in the seperation. However, I quickly discovered what was wrong. I didn't use enough water! I did the Wyeast instructions the first time and frankly, they don't use enough water. The more water you use, the more mason jars you will need, but I think it gives a quicker seperation.
So, the second time I did this, I used more water to swirl the trub in the bottom of the fermenter and then poured it into two mason jars. It only takes 15 minutes for the hops/bad stuff to settle. If you look VERY closely at homebrewer_99's picture in his post, you can see about mid way up in the jar, you will see a line between the ever-so slightly "greenish" looking trub below and the suspended yeast above. When you pour the suspended yeast into a new jar (after 15 minutes) DON'T pour that greenish looking stuff. You will definitely notice the difference in color when you pour.
Do it again 15-30 min later. There will be some more trub the second and maybe a third time. After that, THEN let it sit overnight or longer. That's when you wait for the yeast to settle before pouring OFF the liquid.