We introduced the rubber cup for two reasons. Firstly, it should facilitate storing and increase the lifetime. After using, please rinse it with the liquid of choice and put the rubber cap on. Please keep it in a vertical position. If you store the RE dipped in the solution, the electrolyte would leak out slowly until the RE is empty.
Secondly, when putting the cup on, you should see air bubbles entering the RE. This means that the ceramic frit is not clogged. If there are no air bubbles, please use fine sandpaper (P600-P1000) and follow a simple procedure from the movie. Please note that the above instructions apply only to the reference electrode with the ceramic frit molten in a glass body. For plastic electrodes, the procedure is different.