Cut off the leaves (also known as fronds.) You want to preserve as much of the light parts of the leek as possible.
Cut off the roots.
Cut the leek in half the long way.
Marvel at how filthy it is! No problem, this is easy to clean.
Fill a pan approximately 2/3 full of cold water.
Dunk the leek into the water. Make sure to separate all the parts so that the water and your fingers can cleanse away the dirt. If you want you can replace the water and repeat 2-3 times but 1x is OK.
Now let's slice the leeks!
Here we have clean slices of leeks ready for your favorite dish!