This is my fifth unit over the years. Worst design ever. Top is problem. It has to be removed completely and put back on with precision or it will fall in reservoir. Also had to run vinegar through it for almost two weeks to remove unpleasant taste. On a good note, works as well as all others I have owned.
Bought the waterpik on advice of my dentist and the person who cleans my teeth. Took some getting used too but once I didn't make such a mess was surprised by its effectiveness. Use it every night after brushing. Mouth feels real clean.
A friend told me to buy a Waterpik ten years ago. I wish I had listened. I saw a YouTube video by a dentist who recommended Waterpik for cleaning crowns. Wow! I am so happy! My friend's Waterpik was ten years old and it needed a rubber gasket in the reservoir. Waterpik mailed it for free. The product and the company are outstanding! I purchased another Waterpik for my twin sister. We are all happy to have the cleanest teeth ever!