Water Level

We have a water level device. It is interesting how it works. 
Here is a description from wikipedia.
Our water level is a bit strange with a fault that is not logical. It works with the two ends near each other, but it looks like that there is less water in it when the ends are two meters from each other. 
My mum just read about a trick about adding some dishwashing liquid detergent. Perhaps it works then...