Hello, the 15ml tank volume is the correct filling volume. However, at the 3 jets per button operation level, the volume is sufficient for the upper or lower row of teeth. In between, you simply have to refill with water or tooth rinsing liquid, which is no problem!

Yes, it is true that the tank volume is tight, but it is enough for 2 jets at the setting. With the 3-fold jet setting, the tank must be refilled, but this only takes a few seconds.