So far I have only worked with dry yeast.
At the end of a batch I split the remaining yeast in half. Half I used it directly in another batch and half I washed it. That's how I was left with only a little yeast on the bottom of a jar. That's what I want to start the starter with.
One should know is that you should never rinse yeast with water (actual yeast washing is an entirely different process that uses acid to kill off wild microflora) I covered the reasons a couple of years. It is always better to store cropped yeast under the beer from which is was cropped than to store it under water. Water provides zero protection for the culture. On the other hand beer has a low pH and ethanol. Rinsing yeast with water is probably one of the worst practices ever propagated within the amateur brewing community. Like a lot of dogma, it is difficult to kill.
That being said, the yeast in the Erlenmeyer flask above is cropped BRY-97, which is dry yeast. To obtain a crop that clean, one has to leave at least 500mL of beer behind while racking (I always formulate my recipes so that I can leave around two liters in the kettle with the break as well as a liter behind in the fermentation vessel). The sediment in the fermentation vessel is swirled into suspension and then allowed to rest for a couple of minutes before decanting only the liquid portion into a sanitized container. This process pretty much guarantees that a yeast crop is for the most part hop and break free.