Ordo Hydro Sonic Water Flosser Rose Gold

I have an ordo electric toothbrush which I love so when I needed a new flosser I looked at Ordo which were recommemended by Which? but I came across a problem straight away. I struggled to fill the water reservoir to the maximum amount of water stated in the instructions and then could not remove both reservoirs to empty a small amount of water left in them the following day. I wanted to fill the reservoir with fresh water not mix it with the old water. I have since been able to remove the reservoirs but not at every attempt. My husband could not do it either. Once filled the flosser works very well to clean between my teeth and Im happy with that but how do other people manage to take it apart and then completely refill. The price is very good though.