Which of the following should not be used to draw a sample into a pipet?

Using the mouth to draw a sample into a pipet is not safe and should be avoided. This method poses a risk of ingesting harmful substances or chemicals that could be present in the sample, which is particularly critical in a laboratory setting where various hazardous materials may be handled.

Safety protocols emphasize the importance of using more appropriate and safer methods, such as a vacuum pump, a mechanical pipettor, or a suction bulb, all of which help ensure that samples can be drawn into the pipet without risk to the person performing the procedure. These tools are designed to handle liquid samples safely while minimizing exposure to the user, making them the preferred choices in a laboratory environment.