I use a piece of ridged airline tubing which is about as deep as my QT is attached to a syringe.
This way, I can do two things:
1-If necessary because it/they are sick and in the QT because of this, I can feed the fish one piece of food at a time, Incan slowly bring the tip to the mouth and just release one piece.
2.-To answer your question, this tool allows me to also "suck up" little pieces of "stuff" to keep the tank clean and keep ammonia out when added to daily, small water changes.
Some like to cycle their QT and use A piece of live rock and this is fine if you want to spend the time, but it's not mandatory if you do regular small water changes and test for ammonia.
Keep in mind, that if you were setting up a QT for sick fish, you would not have the time to cycle.
Hope that helps, great little tool, used it all the time for different things.