I & some others have done articles on yeast washing you'll find helpfull if you've never done it. Not to mention,if you've just used a fancy liquid yeast you hate to just toss out. Dump in 2cups or so of boiled & cooled water to rinse the yeast & trub off the bottom of the FV. It gets compacted down pretty good,so swirl it around quite well to loosen it all. I pour it into a 1/2 gallon kosher dill jar I washed out for doing this. Then proceed as instructed in the article.
If you're just using a common dry yeast you'd just rather dump,then put enough water in the FV to swirl it all up into suspension & flush it. I then proceed to dump in 3TBSP PBW & fill with water to just above the krausen ring. Stir well to dissolve the PBW& let it sit a few hours to soak loose all the gunk. Whipe with soft cloth or a bottle brush (gently) to make sure the sides are clean,dump & rinse.