You should always use a clean vase for your flowers.
Sometimes you will find that your vase has a build up of grime that is hard to reach, especially when you have a narrow or tapered vase.
Try this easy tip - fill your vase with water, add one tablet of denture cleaner, eg Steradent. Let the tablet dissolve and then rinse your vase with water.
You will have a sparkling clean vase ready to fill with fresh flowers.