The Erlenmeyer flask, which is also known as the conical flask, should be rinsed periodically using the deionized water because the Erlenmeyer flask is used for titrations and most of the titrations involve ions. Cleaning the Erlenmeyer flask with normal water will lead to the addition of the extra ions and this will disrupt the titration readings. Hence, the conical flask should be cleaned with deionized water to obtain correct results.